Page 32 - May 2019

• Increasingnosedowncontrolforces; • IASDISAGREElight;
• ALTDISAGREElight;
• FEELDIFPRESSURElight.
A Typical Runaway Stabilizer Trim Procedure:
Control column...Hold firmly Autopilot (if engaged)...Disengage
Control pitch attitude with control column and main electric trim.
If runaway trim stops...End of procedure If trim continues to run away:
Stab Trim Cutout switches (both)...Cutout If the runaway continues:
Stabilizer trim wheel...Grasp and hold
Stabilizer...Trim manually
Training guidelines for the Boeing 737 Max likely didn’t emphasize the new MCAS anti-stall program or provide a pilot- alerting function because it was believed that current protocols to deal with other stabilizer and trim failures covered MCAS failure modes. Why they didn’t have the MCAS listen to both AOA sensor inputs through a comparator, however, is perplex- ing. This being the case, it seems there are a few possibilities to explain the recent unrecoverable catastrophic failures.
One – pilots are not recognizing the failure mode or if they do, are not using the approved procedure that should remove
power from the MCAS. Two – pilots recognized the failure mode but are executing the procedure improperly, too late or the procedure when applied didn’t work. Three – it’s not the MCAS system that is malfunctioning at all, and there exists an unknown and unrecognized failure mode in the Max flight control system yet to be discovered.
When the Ground Gets Bigger
Magazine article lead-times are long (it’s almost the end of March as I write this), and by the time you read this we will have some answers and a solution will be in place. Probably new software, additional AOA sensor input, system activation annunciation and additional aircrew training. Then we can all shake our heads in disappointment over pilot errors, engineering decisions, or the discovery of an unknown failure mode – or a combination of all of the above. However it unfolds, when any failure rears its head in the airplane, it will be, as it has always been, your training, experience, determination and judgement that will be working the problem. And the folks that made those 10 million engineering and design decisions regarding your airplane are not the ones that will be watching the ground get bigger as you demonstrate some of that pilot stuff.
Kevin Dingman has been flying for more than 40 years. He’s an ATP typed in the B737 and DC9 with 23,000 hours in his logbook. A retired Air Force major, he flew the F-16 and later performed as an USAF Civil Air Patrol Liaison Officer. He flies volunteer missions for the Christian orga- niz tion Wings of Mercy, is employed by a major airline, and owns and operates a Beechcraft Duke.Contact Kevin at dinger10d@gmail.com.
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