Flying a Jet
People will tell you all sorts of nonsense about flying a jet – how you need to be some steely-eyed superhuman with reflexes of a cat with over 5000 TT in piston/prop aircraft before you dare to fly a jet.
What nonsense. There is more nonsense in aviation than almost any other activity I can think of, with the exception of child rearing or offshore boat racing. Not sure why. It’s merely applied high school physics.
If you want to look at some good flight training – with admittedly very carefully selected candidates – look at the military. They send kids up solo in F-18’s that don’t have enough flight time to fly a C206 in the civilian world.
In a lot of ways, a jet (either turbo-fan or turbo-jet) is a hell of a lot easier and simpler to operate than a piston/prop aircraft. For example, the C421B’s that I fly are much more complicated than the L39’s that I fly, and have a much higher workload on departure and arrival. You won’t hear any of the aviation blowhards let you in on that little secret – either because they don’t know it, or they’re trying to make what they do seem terribly complicated, either out of insecurity or outright incompetence. Assholes.
A jet doesn’t have prop controls. It doesn’t have mixture controls. It doesn’t have carburetor heats or boost pumps. You don’t have to worry about keeping the engine temps up in the descent. So in a lot of respects, flying a jet is much simpler – fewer arcane systems to worry about.
So. For a guy coming from the piston/prop world, what is new and/or challenging about flying a jet? Good question.
Starting the Motherfucker
You can have plenty of grief starting a piston engine, even on a lawnmower. You wouldn’t think it would be hard to make gasoline burn. Often the hardest thing about flying an airplane (especially an older one) is starting it. If you start it for me, I can probably fly it for you!
Same thing with a jet (turbine) engine. What you need to remember is that a jet engine generally doesn’t like a tailwind when it starts. There are exceptions (the L39 is a honeybadger about a tailwind during start – it just doesn’t care) but many western jets may prefer a little wind on the nose (and not up the tailpipe). The reason why is called a “hung” or “hot” start, where you are pouring fuel into the engine, and it is burning and creating heat, but for whatever reason, the air is not yet moving promptly through the engine, from the front to the back.
During the start, you must carefully monitor the exhaust / tailpipe temp, and be ready to cut the fuel off, if the temp goes over limits during starts. You want to memorize exactly what those limits are. No time for reading a book at this point.
Once you get a good start, life is pretty simple with a jet. No complicated run-up as with a piston engine – just line up, check the percent RPM and go.
Things Happen Faster
This is one complaint (?) that I sometimes hear, about people moving up to more advanced aircraft - and not just necessarily jets. I have trouble understanding this. Faster is like more money. It’s a good thing. Trust me on this. If you’re the sort of person who gets behind an aircraft, trying to fly a 172 (or Mooney) on downwind, well, maybe you should consider some other activity than flying an airplane.
Yes, things happen faster in more advanced aircraft. This means you will be less bored. And the same skills required to fly even a single-engine Mooney or Bonanza or Comanche will be required to fly a jet. Mentally, stay ahead of the aircraft. Have a plan of what you are going to do. Some people call this “flying by the numbers” and is a really good idea for a new jet pilot.
The good news about a jet is that you can brutally pull the throttle back for a descent, and you won’t hurt anything, as you would in a piston aircraft. No silly CHT’s to keep in the green.
I should mention that the higher indicated speed of a jet means that you will probably have a little bit more trouble maintaining precise altitude (see the lift equation) when you are hand-flying on instruments and will probably need to use more bank than you are used to, in order to turn the aircraft. Put another way, delicate hands on the pitch, but be prepared to whack on at least 45 or 60 degrees of bank to get the mother to turn. This becomes more the case as the indicated airspeeds climb through 400, 500, and 600 knots.
I should also mention that flying at very high altitude is very weird. The air is very thin, so your wing is working much harder and your indicated airspeeds can be quite low (even though your true airspeed may be very high) which results in the airplane mushing along.
In fact, the higher you go, the smaller the margin between your aerodynamic (slow speed) stall and your critical (maximum) mach number which is sort of a high speed stall. This is referred to as the “coffin corner”. Google it.
Plugging up the Fuel Control Unit
Turbine engines have a similar failure mode to piston engines, when you stop delivering fuel to them. They don’t work any more. A guy discovered this one day recently on approach to London Heathrow in a two-engine Boeing – he had a double flameout at low altitude after cruising for a very long time at very low temps. The airline, out of habit crucified him, but it turns out that there was a design flaw with the fuel heater which would release chunks of ice into the fuel control unit, plugging it up. Google it.
The fuel control unit is a magically complicated piece of hardware on a turbine which allows the pilot to be a complete idiot with the throttle. It is very sophisticated and will deliver just the right amount of fuel - unless it is plugged up.
Another way that FCU’s plug up is when the pilot forgets to tell the FBO to put Prist in the fuel. To save a penny per liter, FBO’s don’t put Prist in Jet-A. You must ask for it. And, you cannot simply dump it in the top of the tank after refueling – you must add it as the Jet-A is pumped in. People that have forgotten to ask for Prist have had very bad days when they have had double-flameouts at cruising altitude, where it is really cold and the water in the fuel freezes. Prist basically contains alcohol (to mix with the water) and additionally stops crap from growing in your tanks. Ask for Prist when you buy Jet-A.
You will be surprised how much fuel that jets burn at idle. Try not to waste a lot of time on the ground, doing that. You will also be surprised how much more fuel that jets burn at low altitude vs at high altitude. This is very different than with piston engines. If you fly a jet, you will likely want to get up to high altitude as soon as possible.
You will also be surprised at the winds that you will find at high altitude. 100, 150 and even 200 knots of wind aloft can be found. Tailwind is nice, headwind not so nice. Also the turbulence near those speedy winds might surprise you.
You must worry about this stuff, and not run your jet out of fuel.
One failure mode of a turbine engine that will be new to you is the compressor stall, when air stops moving smoothly through the engine. This is not a good thing and can make truly frightening sounds and emit flames. The engine can flame out and require a restart. It can even be permanently damaged.
This kind of thing is very type-specific and you want to carefully read and memorize what your POH/AFM/QRH has to say on this subject. Memorize your air start procedures. Some engines are more susceptible to compressor stall than others.
Air Inlet Icing
If you look at the front of a jet engine, you may see a
metal ring around the inlet. If so, in
the cockpit you will be able to route hot bleed air from the turbine to that
inlet metal ring, to heat it and melt ice forming there. Read your POH/AFM/QRH and it will tell you
when to turn it on. Note that this will
reduce your power available (e.g. for takeoff) and will change your numbers. Google “Air Florida Flight 90”, that had a
bad day in 1982 at
Throttle & Power Management
The big difference – and what you will have to learn about – between piston/prop and jet engines is that you must be more intelligent with the throttles with a jet.
A piston/prop aircraft will tolerate a complete idiot on the throttles. You can jam them all the way forward and pull them all the way back, over and over again, all during the approach. While this PIO’ing will really shorten the life of the hardware, such crappy throttle handling can result in a safe landing with a piston/prop aircraft because the aircraft is relatively light, has plenty of drag, and has instantaneous response to throttle movement.
However, such idiotic throttle work will kill you in a jet, because it is heavier, slippery and may have considerable lag to large throttle movements. A jet will not tolerate a “throttle jockey”.
Even in piston/prop aircraft, I teach people to NOT be throttle jockeys. You should have a nominal power setting in mind for approach, and you should strive to leave it there. If you learn good throttle habits with a piston engine, the transition to a jet should not be a difficult one.
For example, in the Pitts I pull the power all the way off on downwind abeam the runway threshold, and if I fly the descending base-to-final slant “U” correctly, I should not have to touch the throttle again until taxiing after touchdown. The nominal power setting is none.
In the C421, I use a constant 21 inches and 1800 RPM for approach, and control my airspeed in the descent with the timely application of drag (gear, stages of split flap).
In the L39, I use 83% N1 if I am light on gas, 85% if I am fat with gas. Again, gear and flaps as required to add drag to give the correct airspeed on approach.
If I am in a jet and the student is sawing away at the throttle on final, I tell him to overshoot because we are about to die. Not so much because of a stall – though that is a possibility – but more likely because of developing an uncontrollable sink at low altitude which is unrecoverable without afterburners.
Ask the guy that crashed the T-33 short of the 8,000 foot
If you’re an EE, you can probably hear a PID loop, screaming to be let out. Even if you’re not an EE, you probably should know that you are in the control loop business now.
This is what I tell people who want to fly a jet: you need to learn to NOT be a throttle jockey. The way you do this is by cutting the vertical tube in your shower from the valves to the shower head, and insert a 50 foot loop of rubber hose in, clamped at both ends.
Now get into the shower and try to set the temperature. At first you will be sawing at the temperature valves, miles behind the control loop because of the lag created by the long rubber hose.
However, after a bit of practice, you will learn to set a nominal setting which will result close to the temperature that you want, and you will learn to restrain yourself from large over-controlling of the valves.
When you can learn to control the water temperature in the shower as described above, you’re ready to go fly a jet.