Helicopter Turbine Transition - Turbine Transition

Turbine Transition

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Transitioning to Turbines is a personal choice, there's no such thing as as an FAA rating or requirement for specialized training in turbines. Anyone claiming an FAA certified course is doing so purely as a sales gimmick, though it is possible that a Part 141 school may have an approved course. To transition to turbines is simply a decision of further education, and it is a good decision. One of the most important considerations for a Turbine Transition is whether or not you will actually be starting the aircraft, and flying from the designated pilot seat; if the answer is no to either of those, you should reconsider as you'll be wasting your money.

If you won't spend 100% of your time in the right seat and start the aircraft at least once per hour, you're not gaining enough of the experience needed to be worth the money your spending. Some people will tell you that they don't want to start the aircraft to much because it will cycle out. The fact is however, if an aircraft is not started more than once per hour it will not "cycle out" anyway. Besides, you are paying for your time and starting and shutting down the turbine is one of the two most important elements in turbine transitions; the other is torque. Obviously you can already fly a helicopter if you have a rating. The "cycle out" issue in turbines only applies to the hot section of the engine, nothing else. The torque issue with turbines is that the engines often put out much more power than other components are designed to withstand. When you over-torque a turbine, it's not uncommon for the maintenance costs to exceed several hundred thousand dollars. This is why I always stress to students to learn to heed the limitations of the training helicopters they fly; it builds good habits that transition well into turbines.

If you'll pursue a career in helicopter aviation, at some point a transition to turbine powered helicopters will be necessary. In many cases operators will not employ a pilot who has not had at least some training in these helicopters. Often this is a roadblock that many aspiring helicopter pilots face. Is a transition necessary and/or worth the money? That topic is discussed at the bottom of this article in more detail.

Back to the Basics

There are reasons for the basics, if you want to keep the rotors straight and on the top side. I always got frustrated when my students would throw the nose of the helicopter over on departure, and then yank in a bunch of collective to prevent a sink (poor piloting skills). Even in a piston helicopter, this often results in an over-torque, but no ones usually knows it because they don't know what torque limitation in a piston powered helicopter is, they only know about manifold pressure, but there you have it; "never use the collective to fix a cyclic error". Often even pilots who should know better develop bad habits over time, all too often pilots become bored and begin to fly sloppy.

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(In the photo, Rolls Royce 250 C28 engine) By the time you're ready to transition to turbine powered aircraft you should already be a good pilot and capable of maintaining altitude and heading. During this training, you need to focus on the turbine idiosyncrasies. The few hours you will spend in turbine transition need to be about the differences of flying these aircraft; basic flight training doesn't need to be a part of it. I expect that when a heading and/or altitude is assigned, at this level of flying; the pilot will be able to maintain it.

Turbine engines are less forgiving to pilot mistakes than a piston engine is, that's why most operators won't hire a pilot without at least some turbine experience. Remember that a hot section repair on these engines can easily cost $150,000 dollars and even much more. One screw up and the engine is toast.

Torque and temperature are critical with turbine helicopters. Some pilots get into bad habits of rapid shutdowns with piston engines and this bad habit will follow you and haunt you. In fact many habits that you develop as a student and as a pilot building time will be hard to break. It is far better to follow checklists and do it right habitually from the start. In the commercial world when you do something foolish to save time unnecessarily that could damage a valuable helicopter, it could cost you your job. There are people watching you who know!

From the beginning of training and forever, remember this: Never use more power, or fly riskier than is necessary for the operation at hand. By this I mean don't use 24 inches of manifold pressure to do what you could with 22 inches, or 100 percent torque where you could have used 80 percent etc. There is no benefit to aggressive flying when it is not necessary.

What is Different When Flying Turbine Helicopters?

Just everything. The machine will fly the same; maybe easier, but other than that it is all different. The start up, the shut down, the instruments; it's all different.

In the turbine helicopter there are three instruments that replace the manifold pressure gauge that you are accustomed to in the piston helicopter. These are the torque meter, the TOT, and the N1* tachometer. Although the torque meter is primary, any one, or all three of these can be the limiting factor on how much power (collective pitch) is available. Note in the figure (link to the left), these instruments are stacked in the panel.

Also, Instument Panel Figure the tachometers are N1 (the gas producer turbine, aka NG), N2* (the power turbine, aka NP), and Nr (the rotor tachometer. The TOT, is the Turbine Out Temp. N2 is similar to the engine tachometer in the piston aircraft, and is also co-located with the rotor tachometer. N1 is a separate tachometer. The gas producer turbine has no mechanical connection to the power turbine, hence the separate tachometer. See figures instrument, and turbine engine.

There are some very critical areas when flying turbine helicopters and most important are the Torque and TOT. It is very easy to overheat a turbine engine especially during the start process. A turbine engine typically turns at around 50,000 rpm and is not self-sustaining below about 55% N1. With a fully charged battery, the starter will only turn the engine at a maximum rpm of about 15-20% N1 so it takes a combination of the starter and fuel-burn to complete the start process. The entire start process must be completed in about 45 seconds total, and it is absolutely imperative that the starter button is not released until the start process is completed. In normal conditions, the start process takes about 27-34 seconds.

On most turbine helicopters there is a telltale TOT light and on some there is a telltale torque light. Once these lights come on they cannot be turned off except by maintenance. You cannot hide the fact that you over-temped, nor should you desire to hide it.

With the Robinson R66 now on the market, it will rapidly pass the Bell Jet Ranger as the primary turbine transition aircraft. That doesn't change the fact that the instructional methods should not incorporate methods particular to a single make of turbine aircraft when there are better methods that will aid a pilot in transitioning into any other aircraft. Most aspiring pilots will fly many makes and models so they should be taught ways that will better accommodate those transitions. For example, a pilot should not be taught only that aircraft start with modern electronic aids such as FADEC, when many do not. It is important that all pilots transitioning to turbines get their monies worth and understand those differences especially where it applies to other light helicopters that they are likely to be flying in the not-to-distant future like for example the Robinson R66, Bell Jet Ranger, Bell Long Ranger, Bell 407 and the AS 350; all of which have different, but similar starting procedures.

There are many videos on youtube showing pilots doing other things during the automated start never looking at the instruments, but if something goes wrong the resulting hot start will be their fault.

You can jump to the aircraft you will be flying or sections in this article via the links in this list, or just continue reading.

The Robinson R66

The Robinson R66 is equiped with the Rolls Royce 250 C300/A1 engine which has a single stage centrifugal compressor similar to that used on the C30. Though a completely new engine, there are many simularities between the C300 and other Rolls Royce 250 series engines. As with many modern turbine helicopters, the Robinson R66 start is electronically controlled. This means that during the start sequence, you push and release the starter button and the computer does the rest. All you do is monitor the instruments to ensure that a normal start is completed after pushing the fuel control in at 15% N1. It is imperative that the pilot monitors the engine instruments during the start, especially the MGT (Measured Gas Temperature), and be prepared to pull the fuel control to the off position quickly. This is true with all electronicly controlled start systems.

As with all turbines, the MGT/TOT temperature must be noted to ensure that fuel is not introduced to an engine that is to hot, in this case 150°C. If fuel is introduced into an engine at a higher temperature a hot start may occur; at least a rapidly rising MGT is likely.

Aircraft batteries have limited size and capacity. With turbines this is of particular importance because if you can't get enough start speed, this can contribute to a hot start condition. Both the starter and fuel burn simultaneously are necessary for a successful turbine start. Normally, you don't have but two attempts as a start before an GPU will be necessary.

When the MGT begins an increasing trend, that trend can increase very rapidly catching an unprepared pilot off guard. You can get a hot start faster than you can move your hand from your lap to the fuel control. Back to Menu

Start-up - The Bell 206 Jet Ranger and all other helicopters using the 250-C20

During the start sequence, first verify that the throttle is closed by opening it and then closing it to the idle stop, then depress the idle release and close the throttle fully. Turn on the master and verify that the TOT is cooler than 150ºC, if the TOT is hotter than 150ºC then the starter must be engaged until the temp is below 150ºC or it must be left to cool down. In no case may fuel be introduced if the TOT is above 150ºC. In most cases the TOT will drop to less than 150ºC before 15% N1 is reached. Assuming a cool engine, first the starter button is depressed with the right middle finger while the forefinger is held over the idle release in readiness to depress it in the event of a probable hot start. Once 15 percent N1 is achieved the throttle is opened abruptly just past and back to the idle stop. This is the introduction of fuel; the engine will light and the TOT will begin to rise rapidly. The TOT will continue rising into the yellow arc where it will stabilize momentarily until 58% N1 is obtained. The starter button must remain depressed until achieving 58% N1 and then it is released (what ever you do, don't release the starter prematurely). As N1 passes 58% the TOT will slowly decrease back to about 520ºC where it will stabilize for the warm-up.

The basic focus of your attention during a turbine start should be as follows: Verify that the throttle is in fact closed. Turn the master on and verify that TOT is less then 150ºC, then depress starter button while watching the N1 tachometer and peripherally you will notice the rotor begin to rotate at about 10-25% N1. At 15% N1 introduce fuel as indicated above. Once fuel is introduced, your primary focus must be on the TOT and as the TOT begins to decrease then your focus will move back to the N1 tachometer while you wait for 58% N1 when you will release the starter button. The modulated start of the Long Ranger with the 250-C28/C30 engine is different.

There are some variations that may occur during this start. If the TOT increases beyond the yellow arc rapidly, immediately close the throttle while keeping the starter button depressed until the TOT decreases into the green and stabilizes there; then attempt a restart if the cause was other than a weak battery. If the battery is weak get a GPU; do not attempt another start without it!

If you make any screw-ups during the start process, the single most important issue is to keep the turbine cool, don't let it melt down on you, it could cost you your job. You will do this by keeping the starter button depressed, or by depressing it. If for some reason your finger slips off the starter button, depress it again without delay. This will most likely result in a hot TOT and you will probably have to close the throttle and run the start sequence again provided the over-temp light does not come on if so equipped (not all are); if you know you over-temped the engine, then you must fess-up.

Once the start sequence is completed N1 should stabilize between 62 and 64 percent where you will warm the engine for 1-minute, so start the clock and then after 1-minute has elapsed increase N1 to 70%, then turn on the generator and other electrical. The throttle should be retarded back to the 'flight idle' stop after turning on the generator (see note below). This practice is especially important on aircraft where the throttle is properly set and will not stay at 70%. Let the engine and lubricating oils warm up until all instruments are in the green. Pay special attention to the transmission temperature. Do not take off with any instruments indicating out of the green range. After all instruments are green begin increasing the rpm very slowly, do not exceed 40 percent torque during the increase. If the ground is slippery you better keep it closer to 30 percent to avoid a sliding yaw that you will not be able to stop. Once at full rpm if all instruments are green, you may fly.

NOTE: Usually, people are taught to leave the throttle at 70% once it is advanced to that point, or at least they are not taught to do otherwise. This is really incorrect and can be dangerous. The Fuel control units on these turbine helicopters are spring loaded to stay in one of two positions; either at idle (aka flight idle), or at the wide open position. If the throttle is properly adjusted (friction adjusted only by maintenance), it will move smoothly and it will take a predetermined amount of torque to twist the grip. If the throttle is stiff and/or not smooth, then there is a problem with the linkage or cable. Throttle stiffness is a very common problem with older helicopters. I have even had mechanics tell me that there was no adjustment or spec, but I have also pulled the maintenance material myself and showed them that there is in fact a procedure for checking and setting throttle friction.

The 70% setting was really due to the electrical load back when the C18 was common, since then 70% has really just lingered. Just one of those things that never got changed mostly because nothing is simple where the FAA is involved. There will likely be no negative impact due to turning the generator on at or above idle.

Be certain that the throttle is fully opened, and then do not decrease the throttle on a turbine helicopter in flight, ever (except to control an engine over-speed), and do not attempt a lift off with less then full throttle (100% N2). Utilize the beep switch to adjust the N2 tachometer to 100% if it is not already there; no more than 100%, and no less. Be cautious increasing the N2 rpm with the torque near maximum because a momentary torque increase by 5% may occur and could result in an over-torque. Be aware that in some helicopters, there can be different limitations for different torque settings, for example in the Jet Ranger you may not exceed 85 percent torque above 80 knots.

If you lift to a hover with less than full throttle in a turbine helicopter, and you then attempt to roll up the throttle, you will experience a massive and damaging over-torque. The only correction for low rpm in a hover in any helicopter is to land. Also, if you notice low rpm while in flight, you must reduce collective about 5% before beeping up the rpm due to the impending torque spike.

If during the start sequence the rotor is not starting to turn by 25 percent N1, close the throttle and continue starter operation until the TOT is stabilized. This condition occurs from time to time however rarely, but usually only in cold climates. Normally the rotor will turn on the second attempt. Remember that you only have enough battery power for two start attempts and then a GPU will be needed. In cold climates you may turn the main rotor backwards by hand to loosen up the oils in the transmission and the gearboxes.   Do not do this by turning the tail rotor as damage to the tail rotor drive may occur. Turning the main rotor backwards will drive the turbine, and you will hear it. There is no harm in this. Turning the main rotor in the direction of rotation is fine also, however it will not turn all the components in the gearbox. Some companies have a policy against turning the rotor opposite the direction of rotation so be aware of unique policy. Back to Menu

Shut-down

A cool down is important for any helicopter, but with a turbine engine it is even more important. Upon landing move the throttle to the idle position and reset the timer. Remember that (per the most recent Rolls Royce recommendation), it is best to have a cool down between 90 and 120 seconds. Either a longer or shorter cool down leads to coking. If you have idled for an extended period, it is best to run the engine at 100% for a short period before shutting down. Prior to shutdown, the TOT should stabilize +/- 525ºC. Rolls Royce also recommends that immediately after shutdown, the rotor be rotated backwards for two (2) full revolutions to move the hot oil in the engine bearings which will help prevent coking.

During the cool down, unnecessary electrical items may be turned off but leave the generator on. After the timer runs for two minutes use your right forefinger to depress the idle release and close the throttle. Leave the battery on until the rotor is stopped and keep an eye on the TOT for several seconds as you complete your checklist as the engine can flash/flare. If this happens, just engage the starter and ensure the throttle is full closed.

If you inadvertently close the throttle (which requires depressing the idle release) rather than permitting a proper cool down, leave it that way! DO NOT INCREASE THE THROTTLE! If you attempt to relight the engine it will over-temp and I mean fast, and there goes the engine and possibly your job. Shutting down without a proper cool down is not good but it does not require a report to maintenance unless you make a habit of it, which could also cost you your job. A shut down without proper cooling can result in oil coking (hardening of oil deposits on bearing shells), which can cause future engine problems.

Some bad Habits to Avoid

Never use your right hand to to do anything other than control the cyclic except for the start up and the shutdown. Never depress the idle release or the starter button with any finger on your left hand; if you do, sooner of later you will accidently shut the engine down without intention.

From the beginning of flight training you must be honest. If you screw up, admit it. Make the right reports. You will at least sleep well and a good name will follow you even if you do screw up as we all do at times. We are human and we will make mistakes. The only unforgivable mistake is hiding it. I would rather have a reference say that he or she toasted an engine but admitted it, than to learn that they toasted an engine and then tried to hide it. Which do you think sounds better?

Potential areas for mistakes

Failure to recognize a rapid increase of the TOT, and failing to cut off the fuel while keeping the starter depressed to ensure a cool down without an over-temp. Failing to keep the starter engaged until the TOT decreases to the normal operating temperature. Remember that if you happen to release the starter button prematurely, engage it again immediately if the temperature is hot; it will not hurt anything to reengage the starter.

Turbine engines that have been shut down for fueling or other reasons, and that will require a restart before the engine has thoroughly cooled, will have residual heat. Be aware that when you shut down an engine, the temperature actually increases for a short period of time before it starts to cool down; this condition is known as 'hot soak'. You must remember that you must not introduce fuel into a turbine engine when the temperature is higher than 150 degrees C or a hot flash and resulting over-temp may occur. Also, it may not be practical to let the engine cool longer as the job at hand may not permit this. Therefore the following technique can be used to cool the engine prior to the introduction of fuel. First, verify the throttle is closed, then depress the starter button and spin the engine for a short period (often 3 to 5 seconds is plenty), but not more than the percentage recommended for fuel introduction, and then release the starter. This will spin the turbine forcing cooling air through it which will quickly drop the temperature. As the temperature decreases below 150 degrees C, depress the starter again and introduce fuel as you normally would. This reengagement of the starter will not hurt anything, and is often the only way to cool the engine without running the starter to an engine rpm greater than that recommended for the introduction of fuel.

Other facts

A low battery can result in a hot start because the starter will not spin the engine up to an acceptable speed where it can cool and continue to spool. If the engine has a tendency to hot start, cut off the fuel while keeping the starter engaged until the TOT has stabilized in the green or at least dropped into the green zone; only then should the starter be released.

While I was training at the Bell factory, the instructor demonstrated that the sequence of events in an actual engine failure are different then that which we would normally expect. For example, we would expect the 'engine out' horn and light, but what actually occurs first (unless you happened to be looking at the N1 tachometer), is a low rotor speed horn and light if one exists. If you have an engine failure in a turbine helicopter three things will take place; the low rotor horn/light will activate, the power turbine, gas producer turbine and rotor tachometers will begin to decrease (you may get a needle split).

If you are starting a warm engine (one that has not cooled for more than 15 minutes), you may increase the N1 to 70 percent and turn on the generator immediately after the engine has stabilized after the start. If the engine has cooled for more than 15 minutes, then the normal 1-minute warm up is required.

* In some helicopters the N1 is referred to as NG (gas producer tachometer), and the N2 is referred to as NP (power turbine tachometer).

Why the 2-minute cool down?

The cool down allows the temperature to stabilize throughout the engine preventing oil coking, and preventing heat cracks in metal surfaces due to rapid temperature changes. There is no way to measure the actual temperatures at the hottest locations inside the turbine engine, therefore there are sensors placed at specific locations in the outlet stream. It can be safely surmised that if the temperature in these locations are within a given range, then the temperatures in the hottest locations are also within a given range.

Long Ranger Modulated Start

I would rather start the Long Ranger than the Jet Ranger because I have more control over the temperature. Most processes in the Long Ranger start are similar to that of the Jet Ranger except that the introduction of fuel is very gently modulated rather than an abrupt opening of the throttle. If you snap the throttle open on a Long Ranger (206L-x) you will get an immediate hot start for sure. Be aware that the inteli-start system installed on a Long Ranger (Bell 206L-x), does not change the start process at all.

The process: Master on, verify TOT cooler than 150ºC. Depress starter and as the N1 tachometer passes 12% focus on the fuel pressure gage and open the throttle very slightly until the engine lights; you will also see a slight drop in fuel pressure if you were to look at the fuel pressure gage. When the engine lights, you should then focus on the TOT which will increase rapidly; you must manage the temperature in the green by gently rolling the throttle (anywhere below 826 degrees is ok). As the TOT increase speed slows, increase the throttle gently to force the TOT into the yellow, a little higher won't hurt. It will be necessary to keep gently increasing the throttle to keep the TOT in the yellow arc until the release button snaps up and at that point the TOT will decrease to about 550ºC where the rest of the process is the same as the Jet Ranger.

When I was at the Bell factory course, they said that more engine damage occurs from repeated cool starts than from hot starts on the Long Ranger. If you have a cool start it will not likely cause an immediate problem, and it may not ever be a concern unless the cause is clearly your technique and you do it that way all the time. The reason that a particular temperature during the start is desired is the fact that in turbine engines the blades and housings have very close clearances and different metal types for which the expansion speeds vary.

You cannot manually control the temperature during the start in many turbines because this is accomplished through the elecronic system control which is called a variety of different names depending upon the manufacturer, the Long Ranger is an exception. When starting an electronically controlled system, you must monitor the temperature and be prepared shut off the fuel supply should the start go hot. Back to Menu

Hot Start

You must prevent a hot start. There may at times be a tendency for the helicopter to "hot start"; in this case, the TOT will rise so fast that it may be difficult to close the throttle before a temperature exceedence occurs. Contributing causes could be; a weak battery, incorrectly adjusted fuel control, fuel introduction with a TOT near or greater than 150º, or any combination thereof. Note the markings on the TOT in the instrument figure. The lower Red line is at about 770º, and the upper red line at 927º. You may exceed the lower red line for less then 10 seconds; while you may never exceed the upper red line. Either of these conditions will light the TOT light, and you must then shutdown the helicopter for a Hot Start Inspection. The key to successfully starting a turbine engine is knowing the rate of the TOT needle movement. I find that usually the time above the lower red line is about 3 seconds when the engine is started within 15 minutes of shutdown (if it rises above the lower red line at all).

Hung Start

A hung start may occur as the result of a fuel control adjustment or malfunction on the lean side. This will be indicated by the failure of the engine to continue spooling up which will be indicated by the N1 tachometer hanging rather than continuing its increasing trend. The TOT could go hot as well. As in other conditions where the start must be aborted, the fuel must be turned off (throttle closed), while the starter is held engaged until the TOT has stabilized.

Starter Limits

The starter has its limitations as well. In general, this is due to starter overheating. These limits are usually time limits something like; 40-seconds on, 40-seconds off, 40-seconds on, 40-seconds off, 40 seconds on, 30-minutes off. If you exceed these limits, you could smoke an expensive starter. The important issue here is that in practicality you must observe these limitations. This means that you would not attempt to many starts (note battery limits). However if a hot start, or hung start situation arises, you might exceed starter time limits in an effort to cool a hot turbine. It's better to toast a starter that may cost a thousand or two, than to toast a turbine worth perhaps a hundred thousand or more.

Battery Limits

Aircraft batteries are small, and as a result they have very limited performance. Depending on the type of battery, there may be a temperature limit as well. Most importantly, you will only get two start attempts on a turbine helicopter in most cases. If it does not start on the second attempt, find the problem, and get a GPU. One of the most common problems with a failed start is that the fuel valve was left in the off position.

Turbine Engine Cooling

The turbine engine is a constant burn, internal combustion engine. Ignition is provided through the igniter circuit only during the start process. Once the burn has begun, the igniter no longer functions, however fuel flow and burn remain constant. The temperatures inside the turbine section are extremely hot, and primary engine cooling depends on air flow. Approximately 70 percent of the air driven into the turbine section from the compressor is used for engine cooling. As with other internal combustion engines, fuel and oil are the two other sources of engine cooling.

Checklists and Preflight

Preflight - As always, the first flight of the day by a given pilot demands a complete preflight inspection of the aircraft. It may be acceptable after the initial preflight for that pilot to perform at the very least, a walk around inspection prior to each flight, provided that no other pilot has flown the aircraft since his or her last flight. During the preflight or walk around it is imperative to observe all compartment doors and/or panels, to check visible fluids, and to observe for leaks.

Checklists - The use of checklists is mandatory. However, it is advisable to use memory sequences for various tasks where the use of the actual checklist would slow an important, speedy, memory sequence. The checklist should be used to back up the memory sequence once it is completed. In the Jet Ranger, or any turbine helicopter for that matter, an example of a memory sequence is the actual engine start sequence. Example - Right middle finger on the starter button, left forefinger on the timer start button. Depress the timer, then the starter button, then the left hand to the throttle. At 15 percent N1 snap throttle to detent. Watch TOT rise and stabilize, then as TOT decreases watch N1 with the left eye, and TOT with the right (humor). When 58 percent N1 is obtained, release starter button. Observe TOT stable, Check start time. Continue checklist.

The use of memory sequences is important in any aircraft during various phases of flight or checklist use, however these sequences should be backed up by the written checklist. Note that although in the past it has been acceptable to write your own checklist if you so desired, the FAA has taken a different stand recently (2004). The FAA now insists that a manufacturer checklist be available and used. You may still write your own checklist, but it must contain at least the sequence and content of the manufacturer checklist.

Jet Ranger Weight and Balance

If you are one of those people who belittles the importance of weight and balance, you should find a different career. Weight and balance is extremely important. Does the fact that the aircraft is within the weight and balance limits mean that you can fly? Does it mean that the aircraft will fly? No, it does not. There are many other variables that will determine whether or not the aircraft will actually fly in it's current configuration. These include; gross weight, density altitude, temperature, and moisture content of the air (humidity). Other factors include the job at hand such as confined area operations or slow speed flight, where the hazards and/or power demand are higher. Often students are of the opinion that the concerns of weight and balance are relative only to the light aircraft flown during flight training; this is very wrong. I can't tell you how many schools I have visited and heard students poor attitude or regard for weight and balance.

As you move into larger aircraft, the weight and balance calculations often become more complicated than they were in training aircraft. This is due in part to fuel loading. No longer do you have one or two fuel tanks in a simple location. Often you have several fuel tanks of various shapes and sizes placed whereever the manufacturer could find the space for it. The Jet Ranger is no different. You should calculate several practice Weight and Balance exercises. One of which should be the extreme forward weight, and another that would be the extreme aft weight. What is the minimum fuel with which you can fly? Always know your limitations.

Hydraulic Failure

Once you move out of training helicopters it's almost certain that everything you fly will have hydraulics. In some helicopters this may be limited to a hydraulic cyclic, while in others it may be hydraulic cyclic and collective while some will even have hydraulic pedals as well. For example, Robinson R44's 2000 and later models, later Bell 47's and all Jet Ranger and Long Ranger helicopters have a hydraulic cyclic and collective with manual pedals. Earlier Bell 47's had just a boosted cyclic. This is due to the fact that the pedals on light helicopters take very little effort to operate as does the collective. In the event of a failure, these boosted controls become very hard to manipulate.

In all helicopters there are specific procedures for any emergency condition, or occurrence. A hydraulic failure is an emergency situation. The R44, Bell 47, and Jet and long Ranger helicopters the procedures are all similar, and although this article is on the Jet Ranger, this will work in other models. During an actual hydraulic failure the controls will become very stiff and difficult to manipulate. You should attempt to reach a landing area within about 20-minutes of the failure; this is due to pilot fatigue, and you will become fatigued. The landing area should be a smooth hard surface. Ideally an airport but remoteness may make that impossible (solid dirt or grass will work). In any case it should be smooth and level as it will be necessary to perform a run-on landing unless you're better than average. During a hydraulic failure it is imperative that you input less than 50-percent of the control deflection that you would use in normal conditions. Turns and descents should be shallow. It is best to maintain airspeed between 45 and 70-knots.

Actual Failure - KEEP YOUR COOL! Stabilize and get within the correct airspeed range. If necessary, declare an emergency. Upon experiencing the failure, pull the hydraulics circuit breaker (making sure you are not holding pressure on the controls which would result in an excessive input if hydraulics are restored). If hydraulics are restored, continue to the landing area and get your maintenance department to fix the problem. If the effect of pulling the breaker was null or questionably different, push the circuit breaker back in, and turn the hydraulic switch off and continue to the landing area. You do not want the hydraulics coming back on during the actual touch down landing, as it could result in dynamic rollover; therefore it is better to leave the breaker in, and the hydraulic switch off if in doubt. The landing should be a run-on at a speed above translational lift, and at full rotor rpm. Remember that you only have a hydraulic failure, therefore you still have pedal (anti-torque) and rpm control which will remain normal.

Simulated Failure - During a simulated hydraulic failure, the instructor will switch off the hydraulics and you will only simulate pulling the circuit breaker. You will continue to a run-on landing using minimal control inputs. The landing must be a run-on, while maintaining runway centerline.

Hydraulic Failure Rules of Thumb

  • Circuit breaker pulled, reset if hydraulics don't return, then Hydraulic switch off.
  • Shallow turns and descents, half of normal
  • Firm positive control
  • Jet Ranger 61 to 69 knots, different make/model helicopters, different speeds
  • Land within 20 minutes, this is a pilot fatigue issue
  • Shallow run-on landing to a smooth, hard surface Jet Ranger 9 knots approx

Autorotation VNE

Note that on many helicopters, there is the normal Vne which is always indicated by a red radial line on the airspeed indicator. Note that there is also a Blue radial line on the airspeed indicator of larger, faster helicopters. This blue line may, or may not exist. It could be that the limitation is simply stated in the RFM or POH. Also note that the blue radial line has a different meaning in helicopters than it does in airplanes where it signifies single engine MCA.

Why would the Vne for autorotation be less than normal Vne? Remember that the rotor is driven by the up-flow of air during autorotation and therefore if the airspeed is to great, there will be insufficient up-flow to maintain rotor rpm. Obviously this would be indicated by a decreasing rotor rpm in conjunction with an excessive airspeed indication. Know the limitations.

Torque limitations

Remember that the turbine engine puts out a tremendous amount of horsepower and torque. The primary consequence of an over-torque in a turbine powered helicopter is damage to drive train components, and/or mounting or structural damage. Relative to the Jet and Long Ranger helicopters, there is also a second torque limitation for cruise flight. In two blade helicopters a longer mast is necessary to allow clearance for the teetering rotor system. The long mast makes a powerful arm and as a result there is an increase in the upper mast bearing wear, and a degree of mast bending that occurs during forward flight at speeds greater than 80 knots with torque in excess of 85 percent. Industry standard is considered to be 80 percent torque at or above 80 knots indicated airspeed.

Torque limit from flight idle to normal operation during start-up - While increasing the throttle to 100 percent N2, the industry standard is to remain at or below 40 percent torque. You will not find this written as a limitation. If you exceed this limitation while on dry ground, nothing will happen except unnecessary stress on the airframe and components. If however you exceed this limitation while on a dolly or while on slippery ground, the helicopter may spin. In fact you can almost be assured that it will spin. If you permit the torque to exceed 40 percent while taking a check ride either with an examiner for a rating, or with a company check pilot for a job, you may be given verbal training even though this is an unwritten limitation.

The yellow arc of the Torque indicator is the 5-minute limit range at airspeeds below 80 knots. Above 80 knots indicated airspeed, you may never exceed 85% torque due to upper mast bearing wear and/or mast bending.

NEVER PULL THE COLLECTIVE without checking the appropriate instrument. An over-torque on a turbine requires an inspection just like overheating does. If you over-torque go straight to maintenance and report it.

TOT/MGT Limits

The green arc of the TOT is the normal operating range, and the upper limit is 738ºC. The yellow arc of the TOT is the 5-minute limit area and also the desired starting temperature range. The yellow arc begins at 738ºC and ends at 810ºC. At the top of the yellow arc is a red radial line which indicates 810ºC and signifies the maximum operating limitation, and the beginning of the 10-second time limit range which if exceeded will result in a TOT light. 927ºC is the upper limit which if reached will illuminate the TOT light. Note that if the temperature remains between these two red radial lines for 10-seconds, the TOT light will illuminate. I strongly suggest that the throttle be closed after 3-seconds (if it is not already decreasing) above the lower limit red radial line of 810ºC (between the red lines).

If the TOT suddenly tends to be operating at a higher temperature than has previously been normal, this is an indication of a bleed valve malfunction, or other bleed air system malfunction, and maintenance should be notified.

Higher atmospheric temperatures will directly affect the TOT indicated temperature, as will downwind hovering.

Autorotation in the Bell 206 Jet Ranger Helicopter

Regardless of the make and model helicopter you are flying, the entry to a practice autorotation should always be the same: Smoothly lower the collective while applying slight aft cyclic, roll off the throttle, establish the attitude which will result in the proper autorotation airspeed while turning to the landing area; then maintain rpm, airspeed, and visual on the landing area. Do not begin a "hunting" condition for either the rpm, or the airspeed.

In the Bell 206 Jet Ranger, minimum descent airspeed is 52 KIAS. Maximum glide configuration is 69 KIAS with rotor rpm in the bottom of the green arc (controlled by the collective).

Fly by Numbers Technique

Although this technique is preferable and always works, it is not often taught; most likely because most people are unaware that it's possible. This is an absolute method which always results in the same flight profile time-after-time. This technique will work with any helicopter (or any aircraft for that matter) once the numbers are learned.

Torque and Airspeed Combinations (Fly by Numbers) for the Jet Ranger

  • Normal Departure Torque = Same as that required to hover. Airspeed = Accelerating
  • Normal Climb Torque = 80% - Airspeed = 60 knots
  • Normal Pattern Torque = 50% - Airspeed = 70 knots - This is also the same settings for the approach to the pattern
  • Initial Approach Torque = 30% - Airspeed = 60 knots
  • Cruise Torque = 80% - Airspeed as results, usually 115 KIAS. Or torque as desired below 80 percent and resultant airspeed.

Note that the torque values are not about 80 percent etc., they are positive values. This means that if you desire 80 percent, then it is not 79, nor 81. There are other times when the values may be minimums or maximums. For example, let us say that when you are in climb out, you will use 80 percent with a not less than intention. This means that it is better to have 81 percent than 79 percent. During the deceleration to pattern profile, you will use 50 percent with a not more than intention, etc.

Givens and Variables (Fly by Numbers)

Note that while utilizing the "fly by number" technique, there are always two "givens", and one "variable". This is true with all aircraft, rotor or fixed wing. For example, Note that in 1 above, the departure power is equal to whatever hover power was indicated, let us say 90% torque. Torque and rate of climb will be given, airspeed will be variable (accelerating). The rate of climb will be a given because we want it to be consistent until we change to the next profile which will be 2 above. With regard to setting 2, torque and airspeed are givens while the rate of climb becomes the variable.

Note that in 3 above, torque will be given as will be the pattern altitude, while airspeed will be variable. This could be changed if we desired, if perhaps we wanted a given airspeed where then the power (torque) would become the variable.

Power Limitations

When flying turbine powered helicopters it is imperative to understand that especially during the initial pick-up to a hover, and the initial departure from a hover, there are three (3) critical instruments that must be observed especially in hot climates or conditions. These three instruments are as stated above: Torque, TOT, and N1. Any one of these instruments can be the limiting factor. In hot climates or conditions, it is possible to "torque out", or "temp out". While it is also possible that N1 may limit power, it is not quite as likely. These instruments must be carefully observed. While flying a turbine you must always keep in mind that these three instruments are what replaces the single instrument (manifold pressure) which limits power in a piston helicopter. If you ignore TOT during a hover or departure and it exceeds the red line limits, the TOT light will illuminate, and then the hot section inspection is required.

Note also that it commonly takes significantly more power to terminate an approach to a hover (especially in confined areas), than it does to hover, or to depart from a hover. You must plan this, and if you will be returning with a near similar weight, you may have an issue in the termination which could also result in a hot TOT.

Bell 206 Pilot's "Rules of Thumb"

  • Always keep feet on pedals, right hand on the cyclic, and left hand on or near the collective, whenever the rotors are turning.
  • For a given power setting, there is about 300 pounds difference in gross weight for IGE and OGE hovering.
  • At a given gross weight, approximately 10% more torque is required to hover OGE than IGE.
  • 1% torque equals approximately 30 pounds of weight carrying ability.
  • 1% torque is lost with each 1.5ºC rise in temperature.
  • Approximately 3% torque is lost with each 1000 feet gain in altitude.
  • 1% torque equals about 4 shaft horsepower.
  • N1 is affected primarily by temperature.
  • Torque and TOT are functions of temperature, altitude, and humidity.
  • Fuel consumption at MCP will usually be 25-28 US Gallons per hour.
  • OGE hover is considered to be any altitude above IGE, but more specifically, above 1/2 rotor diameter in height, or about 17 feet above ground.
  • Use Anti-Ice whenever the OAT is at or below +4.5ºC (+40ºF) regardless of visual moisture.
  • For an autorotation to the ground, the helicopter should be level and at or near touchdown before the rotor rpm passes below 70 percent.
  • The autorotative glide ratio is approximately 4:1 at 69 KIAS (Max. glide distance).
  • Visual abrasion on trailing-edge outboard surface of the tail rotor blade(s) indicates track and balance problem.
  • A lean fuel control will cause slow starts in cold weather.
  • A rich fuel control will cause hot starts in hot weather.
  • If a low steady growl persists in the cockpit, check tail rotor for an out-of-balance condition.
  • The Bell 206 (or any US helicopter) will land on a steeper slope with the right skid upslope than with the left skid upslope in a neutral, lateral CG cabin loading condition. Why? Because the cyclic is displaced slightly to the left countering translating tendency which reduces available left cyclic. Some will argue that the mast is tilted to counter this, which is partially true; but it only compensates for it to some degree, not fully.

Bell 206 Jet Ranger Pilot's Checklists

Engine Pre-start Check

  • Seat belts - Fasten
  • Flight controls - Freedom of movement and centered
  • Pedals - Adjusted and centered
  • Collective - Full down
  • Throttle - Check full travel, close to idle stop, and then close to cut-off
  • Landing lights - Off
  • Engine Anti-icing switch - Off
  • Hydraulic control switch - On
  • Radios - Off
  • Fuel Valve - On
  • Instrument cluster - Check
  • Instruments - Check, set altimeter
  • Overhead switches - Off
  • Circuit breakers - In
  • Battery - On (Off if using external power)
  • Caution lights - Check and press to test. Check engine out audio. Raise collective , check low rotor rpm audio signal. Lower collective to full down.

Engine Starting and Run-up

  • Throttle - Confirm fully closed at cut-off
  • Main rotor - Confirm untied and clear
  • Starter - Engaged. Engine oil pressure indication
  • Throttle - Open to flight-idle at or above 15% N1 with TOT at or below 150ºC
  • TOT - Do not exceed starting limits
  • Main rotor - Turning by 25% N1
  • Starter - Release at 58% N1
  • Oil pressures - Check rise
  • Stabilize at flight idle for 1-minute
  • External power - Disconnect (if used) Battery On
  • Throttle - Accelerate to 70% N1 rpm
  • Generator - On
  • Engine Run-up Checks
  • Circuit breakers - All in
  • Fuel boost pumps in - Check combined and individual pressure
  • Lights - On as required
  • Pitot heat - On as required
  • Caution lights - Proper indication
  • Instruments - Check normal readings
  • Radios - On as required
  • Engine Anti-Icing - Check operation, leave on if required
  • Throttle - Advance to full open. Low rotor light out at 90% +/- 2%
  • Governor - Increase to 100% N2
  • Controls - Check carefully, boost ON and Off
  • Frictions - Adjust as desired
  • Fuel quantity - Checked
  • Engine Shutdown
  • Collective - Full down
  • Cyclic and pedals - Centered
  • Throttle - To flight idle
  • Frictions - Tighten
  • TOT - Stabilize for 2 minutes at idle
  • Throttle - To cut-off. Check Eng-Out light and audio
  • TOT and N1 - Observe immediate decrease
  • Generator - Off
  • Battery - Off with TOT stabilized and N1 zero
  • Miscellaneous switches - Off
  • Radios - Off

Oh crap! I took my finger off the starter button!

If this occurs (and sooner or later it will), immediately put your finger back on the starter button and at the same time, depress the throttle release and close the throttle, while continuing spinning the engine until the TOT has stabilized. If you do this quick enough, you won't have an over-temp, but you have to be quick. There is no exception to this rule at least while you are in transition training. This usually occurs when the student snaps the throttle to the flight idle position when he or she will inadvertently remove the finger from the starter button.

You will note that although you took your finger off the starter, the TOT might not have risen too rapidly, and it may seem that simply putting your finger back on the starter button might have worked just fine. In fact if this were a cold start (the first start of the day), it might have been fine to just put your finger back on the starter button, however if this occurs during a warm start it will be another story. The reason is the fact that the turbine gets flooded to a varying degree with fuel (depends upon how long your finger was off the button). When secondary fuel occurs at about 28% N1, the TOT may rapidly climb past the lower red line to very near the upper limit. If it hits the upper limit, the light will illuminate, and a hot section inspection will be necessary. If the needle lingers longer than 10 seconds between the two red lines, the TOT light will illuminate.

Securing the Aircraft – Rotor Tie-Down

If the proper checklist has been utilized, every step necessary for securing the aircraft except tying down the rotor should already be taken. In no case should the rotor break be locked to secure the rotor for extended periods of time. If the aircraft will be stored for extended periods, or if the aircraft will be left outside in windy conditions, the rotor must be secured through properly tying it down. If the rotor will be tied down, the pilot must first pull the ignition and starter circuit breakers, or flag the cyclic or cockpit in some manner. Any other person authorized to tie down the rotor or to handle the aircraft must be trained in the proper procedures which must include securing the aircraft and which must also include tying down the rotor. Do not continue tying the rotor without first checking to see that the breakers have been pulled. It is also helpful to put a small sack (a sick sack works well) over the cyclic as another reminder that the rotor is tied.

Note: The reason for pulling the circuit breakers is to ensure that the helicopter is not started with the rotors tied down. Different operators may have different policies on the procedure. If you start a helicopter, especially a turbine helicopter with the rotor tied down, and you open the throttle, the engine will turn the rotor tied down or not. Something will give.

Fuel Sump Sampling of the Jet Ranger

During the pre-flight, to sample or drain the fuel sump, the following procedure is necessary:

  • Pull boost pump circuit breakers
  • Battery switch on
  • Fuel valve off
  • Place container under sump
  • Depress sump button

Fuel System

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The Jet Ranger features a standard 75 gallon, L-shaped fuel tank situated under and behind the rear seat compartment. The fuel tank capacity can be increased to 96 gallons with the installation of a “Ranger Extender” which increases the level of fuel in the tank. The CG constantly moves forward during the fuel burn in the Jet Ranger. It is important to note that with a Range Extender installed and with the fuel level above 75 gallons, the CG moves aft significantly which requires a minimum pilot weight of 200 pounds in order to maintain reasonable control deflection. The installation of a Ranger Extender requires a placard to this effect. (Yellow Bell 407 Pictured)

The Bell 206 Jet Ranger features triple fuel pump redundancy by utilizing two electric boost pumps which lift the fuel to the engine as well as pressurize the fuel system. There is also an engine driven fuel pump which will lift the fuel by suction and also pressurize the system. During normal operations, all systems operate continuously. The engine driven pump does not have the ability to maintain sufficient lifting of the fuel at altitudes above 6000-feet pressure altitude, therefore in the event of a boost pump failure it is necessary to descend below 6000-feet pressure altitude. In the event of a boost pump failure (illuminated caution light), unusable fuel is considered to be 10 gallons.

Due to the above fuel pump limitations, it is also necessary to descend below 6000 feet pressure altitude in the event of a generator failure because battery depletion could result in a fuel boost pump failure as well.

Critical Wind Azimuth

You should know well by this time, the hazards associated with LTE. However, were you told about the "Critical Wind Azimuth"? Probably not, as many do not know about it.

Critical Wind Azimuth figure is from the Bell 206 Jet Ranger POH, and is the same for all helicopters with rotors which turn counterclockwise. The figure would be mirrored for other helicopters. Most importantly, if you will be doing low speed orbits, it is best to make them to the left. If you make orbits to the right, be very quick on the pedals, and maintain some left pedal pressure. During an OGE hover, be very cautious of the direction of the wind.

To Transition or Not?

Is the cost of a turbine transition worth the money spent and the experienced gained? Yes it is, and there is very little debate in this regard. While training, you will need to build all the experience you can. The only flight school who would dispute the need for a turbine transition is one who does not offer it. The fact that a school does not offer such a transition is however no bad mark against that school.

What is the gain in a turbine transition? The bottom line; experience. Just what all operators are looking for. Even if you will be employed by a company who is willing to accomplish the transition themselves, you will go there with some knowledge of how the systems work, what the instruments mean, and how to start the engine, even though your level of experience in the turbine will be minimal.

Why do some people argue that a turbine transition is a waste of time and money? There is no good reason why someone should argue a turbine transition. If the opportunity exists, and you can afford the cost, it is a good idea. The only reason that someone would argue this is perhaps the same reason that someone would argue that a Robinson is not really good helicopter time. Such a person has no legitimate argument, they just don't like the idea, or in the case of the Robinson, they just don't like the aircraft.

Just how much time do you need when you make the Turbine Transition? Well, that is an issue of importance especially for you since the cost is high. You need starts and shut-downs, not hours. The problem with that is the fact that starts of a Turbine engine are expensive. One engine start is the equivalent of one hour of flight time with respect to how it affects the TBO of the hot section. For that reason, most schools sell five to ten hours of flight time, and you may get four or five starts when you really need at least ten starts, and minimal hours since the flying part you already have down. I have even heard of some schools that don't allow any starts. If that is the case, you need to go somewhere else because you aren't going to gain a thing. END. Jump to Top