Automatic Thrust Restoration

[GearDown&Locked]

Can someone explain how an automatic mode which increases throttle setting with altitude in the MD-81 (ATR) kicks in even when throttles are backed after a problem with an engine? Crew error? Bad design?

[Md-driver]

ATR is in indeed an idiotic idea. I beleive it was installed due to noise abatement proceedures in the US. It is to make sure you have enough thrust after a thrust cut back called EPR SELect on your thrust rating panel or a severe temperature inversion/ windshear encounter. EPR SEL allows a further cutback of power than Climb thrust. In the case of an engine failure after thrust cut-back the autothrottle will increase thrust until one engine reaches GA thrust. For operators not using EPR SEL this feature is both unnessesary and potentially dangerous, as in the case of the SAS MD-80 at Stockholm where one engine died on rotation and the other engine had lost power but was still producing thrust ( due to "clear ice" ingestion on take-off). As the aircraft climbed above 350 feet the ATR tried to increase thrust on the only remaining, already damaged, engine. The result was that no engine acceleration was noted only an ever increasing EGT. The engine finally gave up and the aircraft made a forced landing in a feild approx 12 N.m. from the runway.
My tip to you is if you have any kind of engine problems DISCONNECT the autothrottle immediately as a first action.

[Hudson]

Following an engine failure after take off in the 737 some operators wait until the engine failure and shut-down checklist is called for before disconnecting the autothrottle. Others switch off the autothrottle as soon as convenient without specific reference to the checklist first.

Seems to me that if flying with one engine inoperative requires that the autothrottle be disconnected, then why delay disconnecting - especially as leaving the autothrottle connected can lead in to all sorts of trouble on one engine. Viewpoints please?

[lomapaseo]

In the Stockholm incident, one engine simply lost more power than the other. It did not actually lose all power. The ATR sensed the overall reduction in power and advanced the throttles, which was ignored by the pilot what with the aural warning of autopilot ringing in his ears throughout the rest of the flight.

The ATR system made little diffenece in the outcome since even if the throttles remained at their initial settings both engines were destined to fail as they were left in continuous surging.

This was neither the first nor the last similar incident.

[GearDown&Locked]

The Stockholm accident could have had a different ending "if" the ATR system had been disconnected; Of course both engines were surging right after ice ingestion, but reducing throttle on the engines would probably extend their life a bit more, giving just enough time to GA. I'm also aware that the ATR function was unknown within SAS crews, and that may be one of the main issues (along with bad de-icing procedures) of the crash.

This all happened some 13 yrs ago, but my point is: was ATR a "hidden" feature of the a/c's automatic throttle control, and how many "unknown" systems are there on our a/cs today? Can someone be surprised again by some hi-tech-fuzzy-voodoo-logic system that's probably embeded without our knowledge?