On the same aircraft the evening before the crash, a captain at Lion Air’s full-service sister carrier, Batik Air, was riding along in the cockpit and solved the similar flight control problems, two of the sources said. His presence on that flight, first reported by Bloomberg, was not disclosed in the preliminary report.
Makes it seem like there have been other instances of MCAS where it worked appropriately and the crew didn’t have issues with it.
MCAS is not a stall avoidance system. Its job is increase the force required to pull increased angle of attack (the angle between the plane’s nose and the relative airstream). High AoA leads to a stall, but MCAS doesn’t really care about stalls—its job is solely to change the yoke forces so that the 737 Max met an FAA standard which says that a plane must require increased yoke force to pull increased AoA throughout the flight envelope. Don’t think of MCAS (when functioning normally) as ‘pushing the nose down’. That’s the failure mode. Think of it more as pushing against but not overriding the pilot. Remember, the 737 family isn’t fly-by-wire, so there’s no flight control computer to reconcile the pilot’s input with the flight aids’ input. The flight aids also have to actuate a control surface, in this case the pitch trim system.
On the two crashed flights, the likely cause is that the angle of attack sensor went bad and read a very high value, which is MCAS’s cue to add nose down trim to ensure that the yoke forces change in an obvious, expected way. In the wrong situation, that does look to the pilot like the aircraft is trying to dive and kill you.
One thing I haven’t seen any solid information on is whether MCAS spins the trim wheels. The 737 has large manual trim wheels on either side of the throttle quadrant, which turn and click when the electric trim systems modify trim. In previous 737 models, there were other problems which could cause runaway trimming—which were super-obvious, because the giant wheel next to your knee would start spinning wildly. I don’t know the 737 well enough to say if MCAS would also cause the trim wheel to spin, but if so, the checklist for solving the MCAS problem isn’t any different than it is for solving those that 737 pilots are ostensibly trained in.
That’s not to say there aren’t obvious design flaws in the system. I’ve heard it reported that using the electric trim switches on the yokes, the way the 737 is usually trimmed, would only temporarily disable MCAS. That seems to violate the principle of least surprise. There wasn’t redundancy in the sensor data MCAS got (being fed by only one of two AoA sensors). That’s also bad. There wasn’t a warning light in the cockpit (without buying an optional package) to note that there was disagreement between the AoA sensors. That seems very bad.
It’s a bad situation all around. MCAS might have been a bandaid, but it’s not an unreasonable solution to the problem it was aimed at solving. Sloppiness in implementing it, or a failure to think through all the possible scenarios, ended up killing people.
I’m actually not sure anybody disagrees, really. The problems seem twofold: the lesser problem is that lack of sensor redundancy (I mean, probably, I guess at this stage we can’t be absolutely sure) caused it to misbehave. I have a hard time believing nobody involved in the design process raised a red flag at that, but. The far greater problem, it seems to me, is that nobody really bothered informing the pilots of these possible edge case scenarios, which it turns out might not have been so edge after all. I mean, you address that immediately after the bit I quoted, but I’m just emphasizing it.
Undoubtedly—it seems like the sort of thing which should at least get a line in the flight manual.
That’s also why I wondered about how it manifests in the cockpit. If it’s the Classic 737 Rapidly-Spinning Trim Wheels, then there are some deficits in 737 type training, and the same crews might have lost an older, non-Max 737 if it ran into a runaway trim problem at low altitude. (I don’t know what the other 737 runaway trim conditions are, but possibly they don’t happen much at low altitude, whereas MCAS+sensor failure is going to manifest pretty quickly.)
If it doesn’t manifest as the classic 737 spinning trim wheels, that’s much worse, because Boeing shipped an aircraft where the existing problem-solution pair (spinning trim wheels? disable electronic trim) wouldn’t have worked.
Well this is where Boeing’s internal conflicts of interest kick in, right? If documentation and training materials describe a whole new flight control law that didn’t exist in any previous 737 variants, and emergency procedures checklists add new scenarios, then this sounds like stuff that pilots new to the 737MAX need training on. It strongly implies that the 737MAX is a new type that needs certification. Which would be bad news for Boeing, commercially.
As long as they dodge any fines or court cases, they probably come out ahead.
Which is the problem with the system really. When it makes financial sense to do these things, companies are going to do them, it would be silly of them not to.
WOW Air, the low cost budget Icelandic Airline (that was recently acquired by Icelandair) has suddenly shut down, leaving passengers on the hook. At least, I guess, it’s a “low cost” hook.
[edit] Oops, I thought it was acquired by Icelandair, I guess negotiations broke down, which is why they declared bankruptcy
WOW AIR has ceased operation. All WOW AIR flights have been cancelled.
How will I reach my destination?
Passengers are advised to check available flights with other airlines.
Some airlines may offer flights at a reduced rate, so-called rescue fares, in light of the circumstances. Information on those airlines will be published, when it becomes available.
What are my rights?
Passengers whose ticket was paid with a credit card are advised to contact their credit card company to check whether a refund of the ticket cost will be issued.
Passengers who bought their ticket from a European travel agent (within the European Economic Area) as a part of a package tour (a package which includes flights and accommodation or other services) are protected by the Package Travel Directive. Those passengers are advised to contact their travel agent to arrange an alternative flight.
Passengers who may have bought travel protection, or those passengers whose credit card terms may include such protection, may be entitled to claim compensation and assistance due to delays or travel disruption. However, such compensation is often limited.
Passengers may also be entitled to compensation from WOW AIR, including in accordance with European regulation on Air Passenger Rights. In case of a bankruptcy, claims should be filed to the administrator / liquidator.