Why was there no thrust from the engines in the TACA Flight 110 incident?

Question

I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident. Most key issues of the incident are clearly explained in the episode:

• Why both engines turned itself off,
• Why there was an overheating alert after restarting the engines (and they had to be shut off).

But, there was a short period of time between restarting the engines and manually shutting them off when pilots were claiming that (based on instruments) both engines are working (spinning), but there is no power / thrust being generated by them (i.e. plane has no power).

Either I missed something or this small issue was not explained.

What does it mean that engines are working (spinning?), but not generating any power? Does this refer to situations where only compressor fans are spinning in the cold section, but there is no fuel burnout in engine's hot section? Or is it something else?

And what can cause such situation? If I am not mistaken or not missing anything -- episode explains issues with heavy rain and hail that damaged fans, but says nothing about fuel distribution system, engine ignition or any other issue that could cause spinning engine to not generate any thrust.

Answer 1

To generate thrust, engines need fuel and air: a spark will ignite fuel (by getting heat, above the ignition point), which burn with the oxygen in the air.

On this (and other incidents), together with air, also rain (and hail or snow) in the engine, so the spark is not enough to ignite the fuel, and so the engines stop working. So, this is the important factor: air and rain enter in the combustion chamber. It is not a problem of fuel distribution, it is just a problem of not being able to ignite fuel. [On car you have air filters, and air compressors, but also a very different cycle compared to jet engines]

The continuous restart means that the engines will continuously add some sparks, so that if ignition fail one, at next turn the the ignition should start again.

The spinning means literary: the engines were spinning, but this doesn't mean they can get enough energy. The article in Wikipedia tell us that they never reached IDLE power. I think the problem is that rain has blocked many of the sparks in the engines, so the engines ignited only some time, enough to get the engine spinning, but not enough to get power.