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Es gibt in der MD-80 jedenfalls die A/T-Funktion "EPR-Lim", die das jeweils aktive EPR-Limit (TO/GA, CLB, MCT, CRZ usw.) anfährt.
Weil man es sein ganzes Fliegerleben lang noch nicht tun musste?- warum nutzt man nicht die potentielle Energie und geht mit bester Gleitgeschwindigkeit runter anstatt in den Strömungsabriss zu kommen?
Der Schlamassel geht meiner Ansicht nach eigentlich ganz still und leise schon viel früher los. Mit dem langsamen aber kontinuierlichen Geschwindigkeitsverlust. Damit wird das Flugzeug immer langsamer und der AoA und der Widerstand steigt. Evtl. wg. Vereisung. Die Triebwerkswerte bleiben dabei halbwegs konstant: N1, N2, EGT, Fuel Flow. Einzig EPR steigt in dieser Phase ganz leicht an.Jupp, komisch, N1 und N2 runter, EPR runter und EGT schiesst in Himmel.
Auffallend sind diese Peaks in der EPR bevor der Schlamassel dann losgeht.
undEPR Limit (EPR LIM) Mode
Autothrottle EPR LIM mode is initiated by pressing the EPR LIM button, if the autothrottle is already engaged; or by selecting TO or TO FLX on the TRP, pushing the TO/GA button on either throttle, and engaging the autothrottle. The airplane must be on the ground more than 20 seconds to initiate takeoff mode. Pushing the TO/GA button selects the TAK OFF mode of the flight director. Go-around mode is also initiated by pushing either TO/GA button as for takeoff mode except airplane must be airborne or on the ground for less than 20 seconds.
Upper and lower authority limits are provided for throttle control. The autothrottle function provides upper authority limits by means of EPR limit control modes. Lower limit authority is a function of throttle resolver angle (TRA) (not operative when FMS mode is engaged). The upper limit protects against engine overspeed or exceeding EPR limits. The lower limit prevents the throttles from being driven to the idle stops. As a general rule, when the throttles are commanded beyond the lower authority limit, electrical power is removed from the servo motor until a command in the opposite direction is generated.
The autothrottle automatically reverts from EPR limit to airspeed or Mach speed control mode when preselected altitude capture occurs and a non-T/O mode (GA, TO FLX) selected on the TRP. The throttles are controlled to acquire and maintain the value preset in the SPD/MACH readout. Automatic reversion occurs with either or both FD's engaged when the altitude capture occurs and the pilot follows FD commands. The transition is fully automatic when the autopilot is engaged.
Edit2:Engine Thrust Rating System
The thrust rating system provides the capability of selecting engine thrust rating mode for a specific phase of flight. The engine pressure ratio (EPR) limit (target) for the selected mode is computed by the DFGC based on existing ram air temperature (RAT), or assumed temperature, altitude, and the engine bleed air configuration. The computed EPR target, displayed on the engine display panel (EDP), is supplied to the autothrottle system as one of the controlling inputs for automatic thrust management.
Man muss dazu sagen, dass die Autothrottles in vielen Flugzeugen so ihre Eigenarten haben - das geht von "zu harter" Software (Target-Wert ändert sich zu schnell und die Triebwerke "jagen" ständig den optimalen Wert) bis hin zu "zu weicher" Software (TWK reagieren viel zu langsam auf Abweichungen).While the A/T in the MD-80 does move the thrust levers, that difference doesn't keep some crews in the loop. At the airline that I flew 2600 hours on MD-80, there were TWO high-altitude upsets. Both incidents were caused by the A/T reducing power but not restoring it when airspeed dropped over a period of 5 minutes. Both incidents resulted in dual flame-outs, but no injuries. During the investigation of the first incident, it was discovered that the MD-80 at high-altitude would stall BEFORE the stall warning system activated. This lead the captain on to assume he was over critical mach speed and he reduced power to idle when in reality he was stalling and exacerbated the situation.
The MD-80 A/T did the same thing to me one night. Mountain wave activity reached all the way to the east coast of the US on that night. Riding down the wave from the crest, the airspeed increased, and the A/T reduced, as it should. Riding up the wave from the trough, the airspeed decreased, but the A/T never increased. I watched the airspeed slowly bleed off over several minutes as the Captain read a magazine. At .70Mach, I loudly called "Airspeed" to alert the flying pilot to his situation.
Bitter!The BEA reported that there had been 2 similiar occurrences before: On Jun 4th 2002 a Spirit Airlines MD-82 registration N823NK was in flight at FL330 in daylight out of clouds when power was lost in both engines due to overestimated EPR values due to ice crystals blocking both pressure sensors at the engine inlet, the crew descended the aircraft, activated the anti-ice systems and continued to destination, and on Jun 8th 2014 a Swiftair MD-83 registration EC-JUG was in level flight at FL330 in daylight above cloud layer, when the crew noticed the problem, engaged the anti-ice clearing the problem before reaching stall and continued to destination.