PT6 Power lever stop, prior to engine limits

[myfakeaccount]

Last week I was able to hit the physical stop on the power lever without reaching any of the engines limits. Maintenance verified that the FCU stop is being reached. (so not a rigging issue) Gauges have been calibrated.

I'm look for people's previous experiences here, and perhaps an explanation that would deepen my understanding of the pt6.

Our company only operates one a/c of this type, so I have little to compare it to. But we operate many other a/c using a different version of the pt6. (the other model of the pt6 I fly would massively over temp the engine if you moved the power lever fully forward)

Situation where physical stop is first reaches:
- 700 ITT (limit is 750)
- 2100 ft lbs (limit is 2230)
- 99.7 N1 (limit is 101.5)
- 9500', -3 OAT

While looking into this I've noticed that the physical stop can also be reached on the other engine under the same flight conditions. But the stop seems to correspond with the N1 limit. (the other engine reaches 101.5 right when the Power Lever reaches the stop)

My thoughts are that the N1 gauge on the problem engine is under reading by 2%.

Questions I have:
- Does the travel limit at the FCU correspond with the maximum continuous N1 setting?
- Is the FCU stop adjustable or fixed?
- Could a gauge error, even after calibration, account for the 2% N1 that we seem to be missing?

The engine runs well, and is very close to the other engine and the AFM numbers. But it seems strange to me to hit the travel limit of a power lever without reaching any engine limitations in flight.

Thanks for the replies.

[werbil]

Bleed valve not closing on schedule? My understanding is Ng is a factor in amount of fuel delivered to the engine by the governor. Excesssive bleed air means reduced air for CT, low Ng therefore low fuel are the result.

Know of two 114As that had this problem - bleed valve stuck wide open. ITT was not a problem even though firewalled.

[Cardinal]

I'm surpised you were able to hit the stop at such a low altitude and warm OAT. I'm familiar with a slightly bigger PT6A (-67D), but have encountered the stop from time to time - always at or near FL250, in the dead of winter, SAT - 35C or so. The N1 redline for this engine is 104%, and the FCU stop under those conditions has yielded anywhere from 102-104.3%.

[rigpiggy]

Better than the opposite, when the AME's are to lazy to set the stops for max N1. Had a -42 that would overspeed before going over the ITT's or Torques. Mentioned to the DOM, the next day fixed.

[tech-line]

Situation where physical stop is first reaches:
- 700 ITT (limit is 750)
- 2100 ft lbs (limit is 2230)
- 99.7 N1 (limit is 101.5)
- 9500', -3 OAT

These figures are great but leave alot to the imagination. Were you c/o a egr to check the margins to start with?
If so you would have had chart figures to compare them to ie
-max ITT 705
TX-2130 etc etc

what aircraft are the engines in? that would say more.
also at minus 3 (pressumably on the gnd) the max power stop should be rolled over to make the fcu unable to reach 99% N1 on the gnd to prevent an overspeed should be limited to 97% it the engine can make target power with this on the gnd then with ram air it is "assured" book quote to make 100% in flight.
so once again the purpose of the run is important to make the correct statement.
In the King air B200 I know that the inertial ice vanes when lowered (if lowered) would also degrade the engine performance) during power assurance check).
as to the earlier statement of a bleed alve bieng open or closed partially you would have flame balls popping out the exhaust (a truely amazing sight) and freaky for the first timers.

[werbil]

bleed alve bieng open or closed partially you would have flame balls popping out the exhaust


No flame balls with the -114A. When stuck wide open just would not make torque. Both engines (two different aircraft) ran OK - higher temps but no limits exceeded and smooth with no unusual noises.