Question about 737-700 engine..

[Ref Plus 10]

Hey everyone, question for those knowledgeable about the 737-700 series engines. I was on Westjet 521 from Ottawa to Calgary last night, and on starting the number 2 engine (starboard), bright orange flame was shooting from the rear of the engine for about 10-15 feet, extending from the engine nacelle to the bottom of the wing. The engine was shut down, checked out by maintenance, and restarted without incident.

I'd just like to know for sure what could cause this. I'm pretty sure I know the answer, but would love to hear what you guys (and gals) have to say about it.

Thanks!!

[fogghorn]

For what it's worth. Those engines are bullet proof, the grsc portion on engines for wj pilots is about 10 minutes long. They essentially start themselves - you cannot over torque or over temp them in flight - jam the power levers anywhere you want, the fadec or whatever controls the engines will not allow out of bounds operation. If any operational parameter gets exceeded (engine or airframe) an email is immediately sent to wj management. Flames out the tail pipe on start up would be indicitive of a soft ware glich.

[Ref Plus 10]

So would a safe assumption be FADEC malfunction and fuel was introduced at too low an N1? Captain mentioned no faults were found on the engine monitoring computers

[Steve Baker]

The post saying that the engines start themselves isn't quite true. The NG is a bit of a mix of old and new. The FADEC is supposed to protect the engines on start from an over temp. The software for this may or may not cut fuel off prior to the overtemp taking place, it will certainly shut the start down after it over temps. The start is similar to older style engines with the captain calling for the co-pilot to start 1 or 2. He then monitors engine parameters, mainly looking at N2. When N2 is above 25 % or no longer increasing above 20%, he brings up the engine start levers and starts a clock, looking for EGT to start increasing. Some completely modern aircraft will start with the push of a single button with the pilot monitoring.

It sounds like you saw a torching or tail pipe fire. The FADEC will not protect against this as there is no rapid rise in EGT. Fuel is cut off by the pilots after the torching is reported by the ground crew. Maintenance would then check the engine monitoring system to determing if any damage was done and everyone goes from there.

[KAG]

On start up the FO would have placed the start lever at 25% N1 - not FADEC. The flame you saw could have been left over fuel collected in the exhaust plenum that caught fire on startup. I believe that burning off is called a tail pipe fire. No fire indications in the flight deck, just from ground personal. Calls for a shut down, engine clearing, then get MTCE to check it out.
Not common, but not a huge deal either.
If it had of been more serious, the trucks would have shown up, and you most likely would have been going down a slide.

[carholme]

KAG;

Good one, I was starting to wonder what Steve was referring to on start at N2 percentages.


carholme

[Norfolk]

Im sorry guys but the fuel is put on at 25% N2

N1 is only a call to make sure the blades are spinning before adding fuel. But you knew that.

[KAG]

opps, my bad, I just woke up. N2.. I don't know what those funny guages are called, I just know where to look...

[twnotter]

I wasn't aware there was such a thing as torque on a turbo fan engine. I was thinking that Boeing used EPR. Due to a lack of propeller there is not too much twisiting of the shaft. On the other hand I could be wrong.

Torque- the measured ability of a rotating element, as of a gear or shaft, to overcome turning resistance.

[Ref Plus 10]

thanks for the edumacation guys. KAG, I think you hit it right on the head. Cheers!

[Steve Baker]

Carholme,
The relevant gauge on start is N2. This is the rotational speed of the high pressure core of the engine. The N1 is the fan speed. Measure of power in jets is engine manufacturer specific as opposed to airframe builder. The GE and CFM engines use N1 as the prime means of measuring power, Pratts use EPR, I don't know what Rollers use.

[carholme]

Steve;

Thanks, it was a polite way of notifying KAG.

Other than the internet crap, have you guys heard any news about forthcoming info on the BA 777?

carholme

[ei ei owe]

Some completely modern aircraft will start with the push of a single button with the pilot monitoring.

My modern Metro III does that.