Are the MD-90's pylon flaps EVER cycled?
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Joined: Mar 2002
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From: N/A
Are the MD-90's pylon flaps EVER cycled?
So, as you may know, the MD-90 has movable control surfaces on the engine pylons called pylon flaps:
When the MD-90 was developed, it was discovered that the larger engines were heavy enough that they made it difficult to recover from stalls in certain situations.
So when the yoke is pushed near full forward position, and (presumably) when certain airspeed/AOA conditions exist, the pylon flaps deploy hydraulically to provide additional nose-down authority.
Here's the thing: They appear to literally NEVER get cycled.
I work at an airport where MD-90s appear constantly, and I've never seen the pylon flaps deployed during control checks. No MD-90 pilot I've spoken with has ever seen them deployed. And three MD-90 maintenance technicians with whom I've had contact each said the same.
Additionally, I can't seem to find a single photo or video anywhere on the web showing the pylon flaps in the deployed position.
So is it true that these potentially quite critical control surfaces are literally never cycled? If so, how in the world can it be ensured they will function properly when needed?
EDIT: Removed an unnecessary word.
When the MD-90 was developed, it was discovered that the larger engines were heavy enough that they made it difficult to recover from stalls in certain situations.
So when the yoke is pushed near full forward position, and (presumably) when certain airspeed/AOA conditions exist, the pylon flaps deploy hydraulically to provide additional nose-down authority.
Here's the thing: They appear to literally NEVER get cycled.
I work at an airport where MD-90s appear constantly, and I've never seen the pylon flaps deployed during control checks. No MD-90 pilot I've spoken with has ever seen them deployed. And three MD-90 maintenance technicians with whom I've had contact each said the same.
Additionally, I can't seem to find a single photo or video anywhere on the web showing the pylon flaps in the deployed position.
So is it true that these potentially quite critical control surfaces are literally never cycled? If so, how in the world can it be ensured they will function properly when needed?
EDIT: Removed an unnecessary word.
Last edited by WhiskeyNovember; 1st December 2016 at 21:57.
Joined: Mar 2005
Aviation Qualifications: Military
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From: Aus
A flight test report I read says the flap deflects 30° down when the stick is full forward and take two seconds in operation. Perhaps it's operation is tide in with AoA, WoW or some other, hence no movement on a ground check.
Joined: Dec 2007
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From: uk
Just found this.
• A pylon flap system, installed on the trailing edge of each pylon, provides increased aircraft nose-down pitching moment in the event a deep stall is encountered.
• Moving either control column to the forward stop activates the system. The pylon flap surfaces move from neutral position to fully deployed. Moving the control column off the forward stop causes the pylon flap surfaces to return to the neutral position.
• The blue ELEVATOR AT LIMIT light on the OAP illuminates to indicate that the pylon flaps and the elevators have reached the full down position, and will also illuminate to indicate full up position of the elevator.
Sounds as if when you do a full movement check if you don't get a blue limit light you have a problem with elevators or the pylon flaps, trouble shoot to find which is not bringing the light on.
• A pylon flap system, installed on the trailing edge of each pylon, provides increased aircraft nose-down pitching moment in the event a deep stall is encountered.
• Moving either control column to the forward stop activates the system. The pylon flap surfaces move from neutral position to fully deployed. Moving the control column off the forward stop causes the pylon flap surfaces to return to the neutral position.
• The blue ELEVATOR AT LIMIT light on the OAP illuminates to indicate that the pylon flaps and the elevators have reached the full down position, and will also illuminate to indicate full up position of the elevator.
Sounds as if when you do a full movement check if you don't get a blue limit light you have a problem with elevators or the pylon flaps, trouble shoot to find which is not bringing the light on.
Joined: Mar 2002
Aviation Qualifications: ATPL
Posts: 9,192
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From: Seat 1A
Didn't look at it much..
Is there a plane with more doodads, oddball fixes and aero tweaks...
Thread Starter
Joined: Mar 2002
Posts: 43
Likes: 0
From: N/A
Just found this.
• A pylon flap system, installed on the trailing edge of each pylon, provides increased aircraft nose-down pitching moment in the event a deep stall is encountered.
• Moving either control column to the forward stop activates the system. The pylon flap surfaces move from neutral position to fully deployed. Moving the control column off the forward stop causes the pylon flap surfaces to return to the neutral position.
• The blue ELEVATOR AT LIMIT light on the OAP illuminates to indicate that the pylon flaps and the elevators have reached the full down position, and will also illuminate to indicate full up position of the elevator.
Sounds as if when you do a full movement check if you don't get a blue limit light you have a problem with elevators or the pylon flaps, trouble shoot to find which is not bringing the light on.
• A pylon flap system, installed on the trailing edge of each pylon, provides increased aircraft nose-down pitching moment in the event a deep stall is encountered.
• Moving either control column to the forward stop activates the system. The pylon flap surfaces move from neutral position to fully deployed. Moving the control column off the forward stop causes the pylon flap surfaces to return to the neutral position.
• The blue ELEVATOR AT LIMIT light on the OAP illuminates to indicate that the pylon flaps and the elevators have reached the full down position, and will also illuminate to indicate full up position of the elevator.
Sounds as if when you do a full movement check if you don't get a blue limit light you have a problem with elevators or the pylon flaps, trouble shoot to find which is not bringing the light on.
In which case, I still question how they can be checked and how it can it be ensured they will function properly when needed.
Joined: Jan 2008
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Likes: 2,030
From: Reading, UK
Thanks so much for finding this. It doesn't seem to specify whether the pylon flaps actually deploy during a control check on the ground. It's possible they only ever deploy while in flight.
In which case, I still question how they can be checked and how it can it be ensured they will function properly when needed.
In which case, I still question how they can be checked and how it can it be ensured they will function properly when needed.
But you can see them move (just) during the control checks here
https://www.youtube.com/watch?v=aiC2-TRBdqI
at about 3:11.
Thread Starter
Joined: Mar 2002
Posts: 43
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From: N/A
But you can see them move (just) during the control checks here
https://www.youtube.com/watch?v=aiC2-TRBdqI
at about 3:11.
https://www.youtube.com/watch?v=aiC2-TRBdqI
at about 3:11.
I swear I must have stared at dozens of MD-90 control checks over the years trying to see those damn things move. Thanks so much for finding the video clip for me.
I knew PPRUNE would come through.
