Originally Posted by
patplan
Something of interest perhaps...
Incident: Sunwing B38M near Washington on Nov 14th 2018, multiple system failures
By Simon Hradecky, created Tuesday, Nov 20th 2018 20:04Z, last updated Tuesday, Nov 20th 2018 20:04ZA
Sunwing Airlines Boeing 737 MAX 8, registration C-GMXB performing flight WG-439 from Punta Cana (Dominican Republic) to Toronto,ON (Canada) with 176 passengers and 6 crew, was enroute at FL350 about 50nm northwest of Washington Dulles Airport,DC (USA) when the captain's instruments began to show erroneous indications. The first officer was handed control of the aircraft as his instruments and the standby instruments remained in agreement. The crew decided to descend out of IMC into VMC as a precaution and descended the aircraft to FL250. Descending through FL280 the weather radar and TCAS failed. The crew declared PAN and worked the related checklists. The left IRS fault light illuminated. The flight continued to Toronto for a safe landing without further incident.
The Canadian TSB reported the left ADIRU was replaced. =====
I have a suspicion that in Boeing 737 Max 8 [B38M] perhaps the LEFT/CAPT ADIRU is constantly being overwhelmed by new routines [i.e. MCAS/AOA related programmings] which may from time to time corrupt the system.
-
Incident: Sunwing B38M near Washington on Nov 14th 2018, multiple system failures
Very interesting information, but raises more questions than answers!
My first question is why did MCAS not activate, unlike the other two cases?
I would speculate 3 possible answers to that:
1. The flight was in autopilot at the time (inhibiting MCAS), and/or FCC was subsequently turned off by crew, or kept on till flaps down.
2. The AOA fault on captain's side may have been nose down (not nose up), so that stick shaker and MCAS were not triggered.
3. On that flight MCAS was active on the co-pilot's flight computer (not captain's side).
They may have survived purely by these chance factors (or good CRM...)
Edit: A question about what happened to the faulty ADIRU: Was it kept and repaired, sent back to the manufacturer, or perhaps handed over to the Canadian TSB? Was this a reportable event, or purely a maintenance issue?