Category: 737 MAX

SMAC250 737 Max Analysis with Ben Bohlman Part 3 Ethiopian 302

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737 Max

Welcome to the show about learning to fly, living to fly, and loving to fly. Today we start a special series on the 737 Max. Although a general aviation podcast we feel this is an important topic which all aviators can learn valuable lessons from. Joining me today is Ben Bohlman and Justin Ash.

Before we begin a quick word from our sponsor.

Preflight Checklist:

Sponsor: Aviation Careers Podcast. Use the coupon code PayItForward and you may receive a year access to the scholarships guide. Quantities limited.

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Cruise Flight (Talking Points): 

  • Ethiopian 302
  • Asked to turn on autopilot but it wouldn’t due to excessive control forces (5lb pitch 3lb roll) 
  • Once the autopilot was engaged, it was left on Command A (the failed side) which resulted in flight control issues due to erroneous AOA values, i.e. the Autopilot accelerated to what it thought was the minimum control speed, which was abnormally high due to the failed AOA sensor. 
  • Autopilot automatically disconnected after 32 seconds due to the airspeed being too low relative to the computed minimum operating speed. 
  • MCAS began as the autopilot disconnected and the flaps reached the 0 position.
  • Autothrottles remained in ARM mode as they were receiving erroneous AOA data. This meant they were effectively at full climb power.
  • The crew repeatedly counteracted the MCAS inputs but did not match the trim run time of the MCAS, resulting in ever-increasing control forces
  • After realizing the continuously running trim, the crew disconnected the electric stabilizer trim, effectively terminating the MCAS involvement
  • Due to excessive control forces (around 80-110lbs for the remainder of the flight), the crew was unable to actuate the manual trim.
  • After a few minutes, the crew turned the electric trim back on in an attempt to retrim the aircraft, but while they did trim the aircraft manually, it also allowed the MCAS system to start trimming again “in the gaps”, which it did for much longer than the manual inputs, effectively worsening the situation. 
  • Crash occurred at 500kts, 40 degrees nose down, and 33,000fpm down
  • At the time when the crew attempted to move the manual trim, it would have taken 40 complete rotations of the trim wheel to return to hands-off control forces.
  • AOA vane never failed, just the heating portion, which is why it showed a rapid then gradual increase as it “drifted”.  Because the AOA resolvers never failed, SPD and ALT flags never showed on the LH PFD.
  • The minimum operating speed values were higher than the maximum speed limits, and the stick shaker value was higher than the MMO of the aircraft (.82).

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SMAC248 737 Max Analysis with Ben Bohlman Part 2 Lion Air 610

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737 Max analysis

Welcome to the show about learning to fly, living to fly, and loving to fly. Today we start a special series on the 737 Max. Although a general aviation podcast we feel this is an important topic which all aviators can learn valuable lessons from. Joining me today is Ben Bohlman and Justin Ash.

Before we begin a quick word from our sponsor.

Preflight Checklist:

Sponsor: Aviation Careers Podcast. Use the coupon code PayItForward and you may receive a year access to the scholarships guide. Quantities limited.

The most recent update includes 26 new scholarships and 17 updates, a new index, and a new “Scholarships for Adults” category.

News And Announcements:

Cruise Flight (Talking Points): 

  • Lion Air 43
  • Flights over previous days reported repeated problems with CA ADIRU and CA ADM, and AOA issues that eventually led to replacement of L AOA (repeat issues are defined as 4 occurrences in 30 days for Lion Air, 3 occurrences in 30 days for Batam Aero Technic (BAT)).  Previous 2 flights reported issues with CAS and Altitude, previous flight automatically recorded 21 differences disagree in AOA (not visible to crew)
  • LNI 43 experienced an IAS Disagree immediately after takeoff, along with the activation of the left stick shaker.  CA transferred control to the FO while running checklists. FO jump seater exclaimed that the aircraft was diving down, flying FO said the aircraft felt heavy, so CA instructed the FO to retrim the aircraft.  CA noticed that the trim kept automatically trimming down without input from the First Officer, so identified a trim runaway situation.  The STAB TRIM CUTOUT switches were placed into the CUTOUT position and the trim problem resolved.
  • The flight continued with the left stick shaker activated the entire flight, no autothrottle, no autopilot, no left side instruments, and no electric trim to its destination.
  • CA wrote up IAS DISAGREE, ALT DISAGREE, and FEEL DIF PRESS
  • CA assumed that the automatic mis-trimming was due to the Speed Trim system, caused by the IAS DISAGREE, so, therefore, did not write up the stick shaker or the runaway trim
  • No AOA DISAGREE message displayed, though it is assumed that would have been written up had it been available.
  • Lion Air 610
    • CVR 610 experienced AOA fault of 21 degree disagree, which started during the takeoff roll (FO was 13 degrees up). 
  • Flaps were extended, which corrected the MCAS Auto Trimming.  Aircraft was at 306-318 knots indicated.  56-68 kias over max extended speed.  At one point, airspeed was 90 kias over max extended speed.
  • MCAS trim resumed after flap retraction and continued to the remainder of the flight.  Captain input consistent and repeated nose-up trim to compensate for the MCAS.  After transferring control to the FO, main electric trim inputs reduced drastically, and control forces went from approximately 30lbs to over 100lbs
  • CAS and Altitude differences on 610 were between 10-15 KIAS and 200-500ft respectively
  • FO repeatedly asked if checklists were wanted to no response from the CA.  CA didn’t appear to be responding or listening to FO checklist challenges when actually reading the checklist
  • AOA installation service tests were inadequate to determine whether or not bias (or calibrated error) existed.  A bias could inadvertently be introduced during installation by the resolver gears and main gear on the AOA drifting during installation.  Basically there are two resolver gears, but if one resolver gear is inadvertently moved during installation, then if the calibration tool is inadvertently moved into the Relative instead of Absolute position on one of the gears, that could result in an inherent bias between the two gears that are not detected by a calibration or return to service test.

After Landing Checklist:

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