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invernyx / md11-bugs

The official bug tracker for the TFDi Design MD-11
https://tfdidesign.com/md11.php
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[BUG] - APU Automatically Shuts Off After Engine Start #262

Closed GR1MMly closed 8 months ago

GR1MMly commented 1 year ago

Describe the bug

Approximately 90 seconds after starting the third engine, APU Air deselects itself and initiates automatic shutdown of APU

Steps to reproduce

  1. Bat/Ext Power ON
  2. Recycle Air controller for proper panel automatic configuration #183
  3. Start APU via ELEC Panel
  4. Turn APU Air On (will erroneously do this automatically IAW the above bug)
  5. Start engines normally
  6. Following third engine start, observe APU Air deselects itself without pilot input approximately 90 seconds after initiating third engine start
  7. This deselection of APU Air initiates the auto-shutdown of the APU (correct function)

Expected behaviour

APU Air should not shut off without direct pilot input. While the FCOM mentions with 3x IDGs powering their respective buses provided APU Air is not being used. This is in reference to the APU Air switch being ON, not if the bleed air is actually required. Therefore so long as the APU Air switch is in the ON position, the APU should continue running.

This feature is designed into the APU for the following scenario: APU is started via APU START/STOP -- starting the APU this way inhibits the APU Air shutdown logic APU Air ON for engine start F/O presses APU Air OFF and does not verify APU shuts down (as it wont based on how it was started) and APU continues to run After 90 seconds of APU Air OFF and all 3x IDGs powering their buses, system will automatically shut down APU.

Evidence

No response

Simulator

Microsoft Flight Simulator 2020 (MSFS)

Crash

No

Phase of flight

Pre-flight

Altitude

0

Agreement

GenericNerd commented 1 year ago

Do you have reference for this? The FCOM isn’t necessarily clear (and can be wrong) but I’m curious as to where you have found this information

GR1MMly commented 1 year ago

Unfortunately there is no specific reference I am aware of. The best I can do is offer personal experience and describe how "APU air not being used" is interpreted.

TheFightingRaven commented 1 year ago

no verification needed, he is the verification and it's in the manual just need to look up the exact logic

AllanBurek commented 11 months ago

To clarify, if the APU is started from the START/STOP button on the overhead, the auto shut down logic is not factored. You can select and deselect APU air all day and it wont shut down the APU. APU auto shutdown via the AIR button on the ASCP is only available if the APU is started with the APU PWR on the ESCP.

turbofandude commented 8 months ago

This should be correct now.