A Boeing 777 was in the news yesterday for exhibiting compressor stall in one engine that compelled an emergency landing. There is video footage of this plane from the ground and from inside it, showing bursts of flame from the rear of the engine during each stall event. In spite of this problem, the pilot kept the engine running, as evidenced by the continued stalling behavior.
This ThomsonFly plane experienced a birdstrike on takeoff, damaging the engine and causing the same compressor stall behavior. The pilot kept the engine running for a good 20 seconds after the onset of trouble; the stall events then ceased, presumably because the pilot had idled the engine (and not because the engine had magically healed itself).
So…apparently an engine in stall still delivers a useful amount of thrust? How much? Is this a case of “not much thrust but we’re screwed if we don’t keep it running until we level off and pick up a bit more airspeed”? Is there a serious risk of really shredding the engine if they keep it running?
Googling suggests that the loss of thrust can be anything from minor to near total.
Minor damage to one turbine blade (in an engine that may contain hundreds) could yield a stalled condition for that blade alone. A serious bird strike could affect a high percentage of all blades, resulting in loss of nearly all thrust.
Yep. Compressor stalls can be a minor nuisance or a big deal. But you don’t see them much in modern engines. I’ve never seen one outside the simulator that wasn’t induced intentionally for training (and that only once in an old war bird).
I saw the Philippines Airlines video yesterday. You may also find this video interesting. It’s a video from Boeing that gives a lot of good information about engine stalls and surges and how to recover from them.
As others said, how much thrust you get depends on the type and severity of the compressor stall, and can be anything from a minor dip to a total loss of thrust.
Passenger jets are designed to be able to continue taking off if one engine fails even when fully loaded with passengers and cargo, so there’s no “we’re screwed if we don’t keep it running until we level off and pick up a bit more airspeed”. If an engine fails it’s an immediate Mayday and the plane is immediately coming back in for a landing, but as long as the other engine(s) stay running, it shouldn’t be that big of a deal. Pilots train for engine out scenarios as part of their normal simulator training and should be able to handle the situation.
On the other hand, if you are in something like a single engine F-16, yeah, you’re kinda screwed.
I assume the pilots in the OP’s links intentionally kept the engines running in an attempt to recover the engine, since many compressor stalls are recoverable. It’s not so much that the needed whatever thrust the engine was able to manage, but rather an attempt to recover normal engine operation, or at least something close to it.
I wonder if he was influenced by a desire to keep the hydraulic power system working normally? Shutting off one engine would have shut off one of the pumps. There is probably (?) 2 independent pump systems on that side, plus a crossover from somewhere else. Some of the systems won’t work at low speeds, some have extra demands at landing etc whatever.
I’d agree. An engine running at idle, generating no thrust, but running an electric generator, a hydraulic pump, and supplying bleed air for the anti-ice and pressurisation, is far more useful than the same engine shut down.
Edit: The loss of the engine and associated loss of the systems I mentioned will typically have no affect on the flight, but maintaining the redundancy is important.
Yes, there’s a serious issue of a malfunctioning engine shredding itself. the crew has to determine if it’s a momentary problem or it’s in the process of self destruction.
It’s FADEC controlled so there aren’t many options for the crew except to reduce power or shut it down. It was hard to tell how violent the exhaust surges were or if any of it came out the front.
These are multi-spool/variable stator engines designed to mitigate compressor stalls. If the events are too violent then the planes are designed to fly on one engine.