MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

[SLF3]

Can the 737 control system support DAL C architecture? Superficially it is duplex at best.

It will be interesting to see whether EASA insist on a demonstration of the unaugmented aerodynamics.

If they don’t like the aerodynamics, want DAL C architecture and resist political pressure to approve the Max saga is not over.

[fgrieu]

Originally Posted by SLF3

It will be interesting to see whether EASA insist on a demonstration of the unaugmented aerodynamics.

Or a demonstration that manual trim is operable by the pilot(s) in all parts of the flight envelope that can reasonably be reached.
Or that the risk of an un-contained fan failure sending shrapnel that severe an essential flight control link is low enough.

[OldnGrounded]

Originally Posted by SLF3

It will be interesting to see whether EASA insist on a demonstration of the unaugmented aerodynamics.

Yes. From the EASA "statement of clarification" on September 27th of this year:

Aircraft longitudinal stability is subject to airworthiness requirements. Boeing has to demonstrate compliance of the 737 MAX airframe with these requirements. Consequences of failures of systems affecting potentially the aircraft stability need to be assessed using acceptable safety analysis methodology also subject to airworthiness requirements. Pilot training requirements are not meant to compensate for non-acceptable design on the compliance and safety standpoint.”

Emphasis added. We shall see what they mean . . .

[Loose rivets]

I assume that was written after the event(s), though it does seem a little like moving the goal posts after a multi-billion $ investment has been given the go-ahead.

[OldnGrounded]

Originally Posted by Loose rivets

I assume that was written after the event(s), though it does seem a little like moving the goal posts after a multi-billion $ investment has been given the go-ahead.

Yes, but I think EASA is more reluctant to "rubber stamp" FAA approvals now than previously, and for good reason.

[GroundedDinosaur]

So, If one uses the MET for one long shot of ANU, going to limit up, then MCAS should fire for 10 seconds of AND, and be done, assuming the MET is never touched again?

[jantar99]

Manual Electric Trim (on the stick)
my best guess

[Deepinsider]

Questions.
During flight testing of a new airplane is the plane
actually properly stalled? i.e. Stick hard back and sinking like crazy.

Or do they just validate wind tunnel / simulator results by 'approaching'
the stall?

What will the FAA / foreign authorities require now to be fully assured
that the Max is safe? (with respect to stall characteristics)

[Maninthebar]

Originally Posted by Deepinsider

Questions. During flight testing of a new airplane is the plane
actually properly stalled? i.e. Stick hard back and sinking like crazy.

Or do they just validate wind tunnel / simulator results by 'approaching'
the stall?

What will the FAA / foreign authorities require now to be fully assured
that the Max is safe?

The reported tracks of the recent test flights appear to show that some 'vigorous' manoeuvres were repeatedly attempted - whether these were solely recovery from MCAS operation or included unmediated approach to stall is not clear.

Does anyone know how the data from such flights might be incorporated into SIM behaviour?

[Bergerie1]

Deepinsider,

Certification stalls are very demanding indeed. Sometimes very unusual things can happen, listen to the last three podcasts by D. P. Davies in this thread! D P Davies interviews on certificating aircraft

And some of the test pilots who post on Proone I am sure will be able to give you details of modern flight testing.

[Deepinsider]

Is there enough data from wind tunnel tests to program a simulator, for test purposes
which then might be validated by initial actual inflight characteristics (although not actaully
getting to the real stall?)

[568]

Originally Posted by Deepinsider

Questions.
During flight testing of a new airplane is the plane
actually properly stalled? i.e. Stick hard back and sinking like crazy.

Or do they just validate wind tunnel / simulator results by 'approaching'
the stall?

What will the FAA / foreign authorities require now to be fully assured
that the Max is safe? (with respect to stall characteristics)

Each new aircraft is stalled in the air in both clean and full flap landing configurations.
The stall speed and stick force gradient is measured to compare with data derived from previous flight tests.

[pilotmike]

Originally Posted by Tobin

That's easy: MCAS will not input multiple trim commands unless it is reset. Tugging on the manual trim wheel, successfully or not, won't do that. It is reset by the use of MET (among other possible conditions), which is why it was driving the trim repeatedly in both accident flights. With the cut-out, MET commands don't register, so MCAS is not reset and does not make further inputs.

So are you suggesting that the only reason both aircraft became uncontrollable and crashed is DIRECTLY BECAUSE the pilots attempted to counter MCAS with trim inputs, albeit insufficient?

Further, that if both accident crew simply ignored the initial MACS input and continued to fly the aircraft with the resulting out of trim state that no further MCAS action would have occurred, and they'd have survived?

It seems a highly ironic and depressing thought that the 2 subject flights only became uncontrollable because the pilots tried to fight the effects of MCAS with manual trim.

[Dave Therhino]

Originally Posted by 568

Each new aircraft is stalled in the air in both clean and full flap landing configurations.
The stall speed and stick force gradient is measured to compare with data derived from previous flight tests.

I assume you mean each new aircraft type or new aerodynamic or control configuration, not every production airplane.

[gums]

Salute!

You may have figured it out, PilotMike.

The MCAS apparently did not simply stop, then resume for the full trim amount. Seems it was trying to activate for the full amount or start over unless use of the trim switches or lowering flaps stopped it. In short, it did not remember where it started and mindlessly kept trimming as long as that AoA value was high.

Gums sends....

[Tobin]

Originally Posted by pilotmike

So are you suggesting that the only reason both aircraft became uncontrollable and crashed is DIRECTLY BECAUSE the pilots attempted to counter MCAS with trim inputs, albeit insufficient?

Yes, that is right. A few months ago, a poster who seemed to have a lot of insider knowledge of MCAS explained its workings. Everything he said appears to have been correct.

Yes, they could have simply flown the plane with 2.6 units out-of-trim. MCAS does not repeat after its initial activation unless one of these things happen:
1) Pilots use MET.
2) The autopilot is successfully engaged.
3) The sensed AOA drops below the activation value and MCAS unwinds the trim it previously applied.

Only #1 was a factor in both accident flights.

From the Final Report, section 2.5.1.2.4:

To recover, the flight crew could: 1) stop making manual electric trim inputs (which would stop resetting MCAS),

[Takwis]

To recover, the flight crew could: 1) stop making manual electric trim inputs (which would stop resetting MCAS),

It would have been rather handy, if Boeing had mentioned that after the Lion Air crash. They were adamant that the pilots weren't trimming enough, though. Much commentary was made, here, about those little comments after AUTOPILOT-DISENGAGE, about getting the aircraft back in trim BEFORE cutting off the stab trim switches.

See "Evolution of Stab Trim Runaway Procedure", 737 Runaway Stabilizer Procedure

[568]

Originally Posted by Dave Therhino

I assume you mean each new aircraft type or new aerodynamic or control configuration, not every production airplane.

Indeed you are correct Dave.
I was up early this morning hence my quick post.

Some B1 test flights also check the rudder trim on 737 NG's,at full flap, to be certian that the rudder trim is to spec.

[PEI_3721]

Dave, 586,
for info BAe 146, Avro RJ, DH 125; every production aircraft was stalled clean and as configured for landing.
Risk was managed by fitting a stall panel for comparing cross side AoA vanes and airspeed; this could be used by any operator.

Flight test / certification involved much deeper investigation, extreme manoeuvres, and harsh pilot handling.
High risk flights had additional display and recording of AoA; the aircraft was fitted with a stall recovery parachute. Crew wore parachutes, cabin doors could be jettisoned for escape.

re-certification of the Max probably ranges these types of flights depending on what is claimed for flight with MCAS inhibited - AoA lockout, unreliable stall warning and speed (ADC), reduced stability margin and different feel gearing.

[MurphyWasRight]

Originally Posted by Takwis

It would have been rather handy, if Boeing had mentioned that after the Lion Air crash. They were adamant that the pilots weren't trimming enough, though. Much commentary was made, here, about those little comments after AUTOPILOT-DISENGAGE, about getting the aircraft back in trim BEFORE cutting off the stab trim switches.

See "Evolution of Stab Trim Runaway Procedure", 737 Runaway Stabilizer Procedure

Or had the AD stated that suspected MCAS runaway could be held at bay by momentary blips (up or down) of the trim switches at < 5 second intervals but warned to expect it to re-engage 5 seconds after last input..