Clarification Requested
 

In preparation for an upcoming interview I came across something that I can't find defined anywhere. Can someone please explain exactly what "engine rollback" is? The original source for asking about this is:

http://www.wweek.com/html/king56-062597.html

After some research I found an Emergency AD on the subject.

I is obviously a reduction in performance somehow...but due to what? Is this just an instrument thing as I understand from the mention of software in the AD or is it really losing power on one of the engines?

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/0dd44fe2beb1f516862571f9006b5dad/$FILE/2006-20-51.pdf

where are you interviewing?

ASA ................. (Included the periods because the message was too short.)

It's occurs when you perform a reduced thrust takeoff only. (hopefully you know what that is). Well FADEC (Full authority digital engine control) for reasons in the software algorithm, commands a progressive reduction in thrust. Most of the occurences happen just prior to V1. You can find the AD on it...its for a B-777 but its a pretty good explanation for it. AD # 2006-20-51...hope this helps

Got it.... Thank you.

depending on what interperetation it may also pertain to an engine start. The ITT will rise as fuel is introduced and the N2/N1 spool up- after starter cutout and N2 stabilization the ITT drops back from the peak (of the start) by about 100 degrees C. I cannot attest to a 777 as I don't fly one, but a CRJ-200 will start and the ITT will rise to about 615 deg C, after N2 passes 55% and the starter cuts out, the ITT will roll back to about 515 deg C as the N2 stabilizes around 62-65%. These are round about numbers and different temp/alt conditions will change the numbers but the overall ITT rise/drop remains the same. Also on the CRJ with a reduced thrust aka "flex" takeoff the TO power will typically be 85-86.5%N1 instead of around 90% (normal TO carats), Climb carots are typically in the 90% range and increase as you climb (obviously these are ballpark numbers as well since temp/alt effect the perf numbers). So depending on the question rollback could have a few different meanings. Since ASA has the -200 it may simply pertain the the ITT "rollback" during starts. Hope that helps more than it confuses, although the facts on the 777 are cool- learn something new every day! As far as in relation to the original link- sounds like the rollback was a computer generated power rollback (reduction). But I am just a newbie...:o

I have always thought of rollback being an uncommanded N1 decrease with an ITT increase (sub-idle state). Flameout is N1 AND ITT decrease.

I have searched FAA documents for the "official" definition, but it is a term that appears to be used to describe a variety of situations where the engine "speed" is decreasing uncommanded.

http://www.airs-icing.org/AIRS_II/AI...06-206-739.pdf

The above is a great white paper on "rollback" due to ingestion of ice. When I am asked this question, I give the example of "rollback" due to ice accumulation/ingestion as described in this paper.

What do you call it if your Ng slowly falls down to 42% with the power level at flight idle in a descent? This happened to me the other day. The worst part was the engine wouldn't respond the power lever inputs after that. I was about to just shut it down, but then I figured I could accelerate up to Vne and ram it up to 51%. That worked, then it responded. I don't think that's normal for a PT6 though. I think my FCU was just F'ed up. Anyone else ever have this happen?

That's odd. Did you try moving the condition levers to high idle? Do you have auto ignition? I can't remember the standard parameters for the PT6 (been over 2 years), but that does sound odd from what I remember.