If it was me and I had an engine failure I would declare an emergency and ask ATC to give me a vector to the nearest suitable aerodrome. Turn the plane and try to restart the engine on the way there.
That’s a good question - the NTSB being what it is will no doubt reach an appropriate conclusion - they’re about the only US Government organisation I’d regard as trustworthy.
Perhaps the crew were sheepish about being caught doing something they oughtn’t and hoped they could restart without diverting. Maybe they didn’t have their heads ‘in the game,’ and got so caught up with restarting the engines they forgot the basics. I seem to remember a Delta(?) aircraft crashing in Florida because the crew were distracted by faulty gear indicator.
N2 (and again, I don’t have a gas turbine rating, so maybe some other dopers can correct me here) refers to the core turbine speed. There are two turbines, the low pressure compressor at the front (N1) and the high pressure compressor at the back (N2).
I too, was taught ‘Fly the airplane!’. The helicopter Flight Examiner commented on that after my check ride, because I told him I needed to attend to an upcoming ridge before I answered his question during my check ride. But the other thing that was instilled in me was ‘Always have a place to land.’ It seems that nearly every flight, my instructor would ask me, ‘Where would you land if you lost the engine right now?’
Flying an airplane at the service ceiling, in and of itself, is NOT a big deal. We do it every day with a full load of people. No special procedures are required.
Some manufacturers push harder than others to get the FAA to certify the airplane to the very edge of its capability versus the regulatory engineering standards. Others leave a little more safety factor.
I read every article linked to. Each has significant errors of fact caused by the person writing it having zero clue what they’re talking about. Don’t be in too big a hurry to believe what you read.
Airplanes get ferried empty more than you might realize. A typical airline pilot might fly a ferry once every couple of months, more for smaller companies. And there’s always a temptation to do something, however small, outside the normal routine because for once you have the freedom to not drive in the exact center of the lane. Professionals resist the temptation; bozos succumb. Those guys were bozos in pilot suits.
There have been 3 incidents now involving that particular aircraft and engine combination in which engines have failed at high (but legal) altitudes and refused to restart. There are ongoing investigations, but the speculation is that somehow the fuel injection computer goes stupid and the engine will NOT relight no matter what.
The other incidents have involved only one engine, which results in an emergency landing, but a safe one. Outside the trade press, those incidents went unnoticed. Landing a jet, even a small one, with zero engines is Hollywood stuff. In the real world, odds are it’s gonna end in a crash even with good quality pilots. The landing itself isn’t hard, it’s the part about managing your glide to end up over a runway at the same time your altitude gets to zero that’s hard. With bozos, well …
The NTSB link. “N2” in a GE CF34-3A1 engine refers to the core speed (the compressor and high-pressure turbine). There is no LPC on that engine, only a single-stage fan (and four-stage LPT), whose rotor speed is “N1”.
Johnny has the correct definition of “service ceiling”. The density altitude (true altitude corrected for temperature and humidity) at which the aircraft cannot climb *at all * is “absolute ceiling”.
cabdude’s explanation of altitude-induced flameouts is correct - the less air you have, the less fuel you can put in or the mixture will become overrich. At some altitude you can’t put in enough fuel to maintain combustion with enough flame energy output remaining to keep the turbines turning.
Ignition is normally used only in starting on a turbine engine, true, since the flame normally sustains itself. It can be turned on manually during icing conditions to guard against water-induced flameouts, though, or during a windmill restart.
BTW - I think the CF34 is a modified version of the TF34 - the same engine used in S-3 Vikings and A-10 Thunderbolt IIs. I wonder if the military pilots know about the core locking issue?
This model of the CF34 is a TF34 derivative, yes. The CF34-8 and -10 are entirely different, but use the same base model number as a marketing ploy. That’s actually pretty common in the industry.
There are enough differences to keep the issue from happening on the military engines - at least, it would have in the 10 million hours they’ve been flying. Look for an FAA Airworthiness Directive at some point.
The Ask the Pilot column this week at Salon.com has some interesting analysis of this incident. I won’t attempt to summarize as I don’t want to screw up the details, but it seems to be a situation where a few small errors compounded led to tragedy.
It’s said that ‘there is no single cause for an accident’. Usually, it’s a combination of things ranging from mechanical failure to weather to poor decision-making that lead up to a crash.
Thanks LSLGuy… I was hopping a big iron pilot would come into this.
If you get back and see this or anyone with a lot of high alt jet time, my question is about restarts.
It is my understanding that a lot of jet engines can’t be restarted until below say, 10-12 K feet. At least engines as would be on a Falcon 20.
Insights please…
Flamed the right engine on my C-310 at 30K + one time and it would not restart until below 9 K due to cold and fuel flow problems.
We had snow falling in the cockpit he he he … I went back and told the boss to not bid on that job, we were not able to operate at that altitude with our equipment on a regular basis…
If you mean a Cessna 310, I hope you weren’t at 30,000+. That’d be flagrantly illegal, not to mention box-of-rocks dumb. In the USAF, 25,000’ was the limit in unpressurized jet aircraft even with pressure breathing sealed-face oxygen masks since that was the highest altitude a pressure mask can keep your blood oxygenation at even 12000’ equivalent. If you guys were using nasal canulas or typical genav oxygen euipment you’d have been looking at blood oxygenation levels of 20K+ feet equivalent. Then again, I spent a few months in the 135 world, and I can recall doing some pretty shady things myself. Youth and ignorance and evil managements make a bad combination, but 135 is full of it.
To answer your restart question …
The relight envelope on typical airliner-type engines extends well up into the 30,000 foot range. As rule of thumb, relights are less likely above 30,000, and the odds improve to essentially 100% by 25,000 assuming no underlying mechanical malfunction.
I don’t have any direct experieince with bizjet engines, but I do know the fighter-type engines I’ve flown had similar relight envelopes even though they had much diffferent intake and fan arrangements. As most bizjet engines are intermediate between fighter & wide-body turbofans, I’d bet the relight performance is similar to the them as well.
Relight requires adequate engine RPM, which can be gotten either from windmilling or from the starter. In most airplanes there is a tradeoff, where gliding at the best glide speed would let the windmilling RPM drop too low for a restart. So you end up descending faster & more steeply than optimal for a glide in order to maintain windmilling RPM.
With other engine(s) still running that’s not such a big deal, but if you’re gliding you’re burning very precious altitude to keep windmilling RPM up.
Some airplanes have APUs you can use to power the starter, others use battery power, while others have no way other than windmilling to get/keep the dead engines turning in flight. Having a high-altitude capable APU with good bleed air output make the situation a lot less pucker-ful. Having other running engines makes it downright comfy.
Since I spent about 30 years in the mapping business and flew high altitude a lot and was very used to it and have over sized lungs by accident of birth and can do stuff you can’t, that does not make me dumb IMO. YMMV
The way I flew was not against the FAR’s. If there is another FAR besides 91.211 that applies to me, please show me as I may be misinformed…
The Air Force is obviously different.
Thanks for the info on the big iron. I did not know that they could restart that high.
Do you ever get to actually do an high altitude restart with an actual engine? Or is the danger of damage to the engine too great?
The latest Aviation Week attributes the issue to core lock, a known issue with some CF34’s and some other engines. When an engine shuts down, the static structures generally cool off faster than the rotors, and it’s possible for a part such as an air seal to seize onto the rotor and prevent its rotation until the rotor cools away from it. Those parts are generally honeycombs that sharp edges on the rotors can cut into, forming a controlled-leakage path (not really a seal).
GE has put a design change in place on the inner balance piston seal and thereby eliminated most of the problem, but there are a number of engines that have not yet been retrofitted, and there is still an issue with interstage seals. Pinnacle, meanwhile, prohibits CRJ’s from flying above 37,000 ft MSL to prevent lean blowout on both engines. Other airlines have no doubt taken note, but the FAA has not imposed any such requirements at this time.