Boeing hopes to have the 737 MAX back in the air by December. But a list of five major requirements issued by the European aviation regulator EASA lets one doubt that the time frame can be kept.
EASA’s checklist includes a number of issues that have been disclosed: the potential difficulty pilots have in turning the jet’s manual trim wheel, the unreliability of the Max’s angle of attack sensors, inadequate training procedures, and a software issue flagged just last week by the FAA pertaining to a lagging microprocessor. But the agency also listed a previously unreported concern: the autopilot failing to disengage in certain emergencies.
We will discuss the five issues below.
It is not clear if EASA will insist on all the points to be fixed:
“Any of these could significantly affect the return to service, but we don’t know if they are actually going to become requirements or are they just items for discussion,” said John Cox, a former 737 pilot who is president of the aviation consulting company Safety Operating Systems.
As usual the regulators will not tell Boeing how to fix the problems. Whatever solution Boeing offers for those items simply has to comply with the general demands the regulations make.
Some of the listed items seem to require hardware changes that will have to be applied to all 737 MAX and maybe even to the older 737 NGs.
We discussed the trim wheel issue back in May:
The 737 MAX incident also revealed a problem with older generations of the 737 type of plane that is only now coming into light. Simulator experiments (video) showed that the recovery procedure Boeing provided for the case of a severe mistrim of the plane is not sufficient to bring the plane back under control. The root cause of that inconvenient fact does not lie with the 737 MAX but with its predecessor, the Boeing 737 Next Generation or NG.
- The smaller manual trim wheels on the 737 NG make it more difficult to trim a runaway stabilizer back into a regular position.
- The larger stabilizer surface makes it more difficult to counter a runaway stabilizer by using the elevator which was kept at the same size.
- 737 NG pilots no longer learn the rollercoaster maneuver that is now the only way to recover from a severe mistrim.
EASA listing the trim wheel issue is the first official recognition of this problem.
The manual trim via the trim wheels is a necessary backup for the electrical trim system which relies on only one motor. If the manual trim can not be used in certain parts of the allowed flight envelope, Boeing has a severe issue at hand.
A 2015 EASA safety finding, previously discussed here, accepted the 737 MAX only because Boeing said that the manual trim wheel was operational even at higher speeds and when the electric trim cuts out. It also promised that its training material would cover the issue.
It is now known that the manual trim, especially at higher speeds, may require more force than an average pilot can apply. The general issue and the difficulty is still not mentioned in the current Boeing training material.
The trim wheel problem seems to be an item where the U.S. regulator FAA and the European EASA disagree:
SHARE THIS POST