Go Back  Airline Pilot Central Forums > Pilot Lounge > Safety
Lion Air 737 Max Accident >

Lion Air 737 Max Accident

Notices
Safety Accidents, suggestions on improving safety, etc

Lion Air 737 Max Accident

Old 11-25-2018, 04:18 PM
  #91  
Gets Weekends Off
 
Joined APC: Mar 2014
Posts: 281
Default

FAA part 25 is readily available in PDF format on the FAA.gov website as is the Advisor Circular AC25-7D (the current issue). I could not find anywhere where the pilots' elevator force is required to overcome full nose down or full nose up trimmable stabilizer force.

The Advisory Circulator did say that with the aircraft stabilizer set at the maximum nose down or nose up position that would not trigger a configuration warning the aircraft should be flyable at the forward and aft CG limits.

The question is then what is the difference between full stabilizer travel and travel required to illuminate the configuration light.
F4E Mx is offline  
Old 11-25-2018, 05:07 PM
  #92  
In a land of unicorns
 
Joined APC: Apr 2014
Position: Whale FO
Posts: 6,401
Default

Originally Posted by F4E Mx View Post

The Advisory Circulator did say that with the aircraft stabilizer set at the maximum nose down or nose up position that would not trigger a configuration warning the aircraft should be flyable at the forward and aft CG limits.

The question is then what is the difference between full stabilizer travel and travel required to illuminate the configuration light.
That's just for takeoff. I'm thinking 25.671(c)
.
"to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems)"

(c)(1)

"(1) Any single failure, excluding jamming (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves)."

Also 25.671(c)(3)
"A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable."

Extremely improbable is defined in 25.1309. "they are not anticipated to occur during the entire operational life of all airplanes of one type".

So - airplane must be controllable if a control surface can runaway to a mechanical stop.

Boeing is in a world of hurt if the MCAS is shown to be Part 25 uncompliant.
dera is offline  
Old 11-25-2018, 05:15 PM
  #93  
Line holder
 
symbian simian's Avatar
 
Joined APC: Nov 2013
Position: On the bus,seat 0A
Posts: 3,215
Default

Originally Posted by dera View Post
That's just for takeoff. I'm thinking 25.671(c)
.
"to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems)"

(c)(1)

"(1) Any single failure, excluding jamming (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves)."

Also 25.671(c)(3)
"A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable."

Extremely improbable is defined in 25.1309. "they are not anticipated to occur during the entire operational life of all airplanes of one type".

So - airplane must be controllable if a control surface can runaway to a mechanical stop.

Boeing is in a world of hurt if the MCAS is shown to be Part 25 uncompliant.
Boeing has been in that world of hurt for a while. It is in the manual that to recover from a stall you need to apply AND trim and reduce power as the elevator doesn't have enough authority.
symbian simian is offline  
Old 11-25-2018, 05:22 PM
  #94  
In a land of unicorns
 
Joined APC: Apr 2014
Position: Whale FO
Posts: 6,401
Default

Originally Posted by symbian simian View Post
Boeing has been in that world of hurt for a while. It is in the manual that to recover from a stall you need to apply AND trim and reduce power as the elevator doesn't have enough authority.
That's a violation of pretty basic Part 25 stuff. The lawsuits will be interesting!
dera is offline  
Old 11-25-2018, 05:39 PM
  #95  
Gets Weekends Off
 
Joined APC: Mar 2014
Posts: 281
Default

"A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable."

So basically we do not know if the 737 was designed to be controllable in the instance of full runaway stabilizer travel or not. The instance of the crash might suggest not.
F4E Mx is offline  
Old 11-25-2018, 05:44 PM
  #96  
In a land of unicorns
 
Joined APC: Apr 2014
Position: Whale FO
Posts: 6,401
Default

Originally Posted by F4E Mx View Post
"A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable."

So basically we do not know if the 737 was designed to be controllable in the instance of full runaway stabilizer travel or not. The instance of the crash might suggest not.
Extremely improbable means that it is never expected to happen to the whole fleet, ever.
If a simple AOA sensor failure makes it happen and there's no compensation method for it, this will be nasty, NASTY, for Boeing.
I would say this failure mechanism is "probable" according to the guidance in 25.1309.
dera is offline  
Old 11-25-2018, 06:34 PM
  #97  
On Reserve
 
Joined APC: Jan 2008
Posts: 18
Default

Originally Posted by dera View Post
That doesn't matter. Moving stabilizers have the same requirements for control forces as trim surfaces.

25.255, 25.655 and I think 25.161, and AC25-7B (or whatever the current revision was today).
I don't think you're reading that correctly. The maximum out-of-trim condition that must be correctable with the elevator is that resulting from 3 seconds of trim operation. This is *way* beyond 3 seconds.

The stab wins, it always does. I don't know of any modern jet where the elevator can overcome the stab in worst case scenarios. This should be pretty well covered in groundschool...

If the elevator always won, we wouldn't need the cutout switches.
314159 is offline  
Old 11-25-2018, 06:43 PM
  #98  
In a land of unicorns
 
Joined APC: Apr 2014
Position: Whale FO
Posts: 6,401
Default

Originally Posted by 314159 View Post
I don't think you're reading that correctly. The maximum out-of-trim condition that must be correctable with the elevator is that resulting from 3 seconds of trim operation. This is *way* beyond 3 seconds.

The stab wins, it always does. I don't know of any modern jet where the elevator can overcome the stab in worst case scenarios. This should be pretty well covered in groundschool...

If the elevator always won, we wouldn't need the cutout switches.
25.671

""A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable"
dera is offline  
Old 11-26-2018, 02:20 AM
  #99  
All is fine at .79
 
TiredSoul's Avatar
 
Joined APC: Sep 2016
Position: Paahlot
Posts: 4,046
Default

Originally Posted by ShyGuy View Post
I still think they need to find the CVR to find out what really happened from a human perspective.
I’m going to take a stab at it and say this crew didn’t fully understand what was going on systems wise.
Previous crews did...or got lucky.
TiredSoul is offline  
Old 11-26-2018, 06:39 AM
  #100  
Prime Minister/Moderator
 
rickair7777's Avatar
 
Joined APC: Jan 2006
Position: Engines Turn Or People Swim
Posts: 39,100
Default

Originally Posted by TiredSoul View Post
I’m going to take a stab at it and say this crew didn’t fully understand what was going on systems wise.
Previous crews did...or got lucky.
Either way, boeing should not have put them in that position.
rickair7777 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
bay982
Southwest
23
03-30-2016 04:29 AM
mike734
Technical
4
08-04-2014 02:03 PM
DC8DRIVER
Cargo
6
03-24-2014 06:37 AM
Freighter Captain
Cargo
0
07-09-2005 09:27 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Thread Tools
Search this Thread
Your Privacy Choices