They didn’t buy the DLC: feature that could’ve prevented 737 crashes was option
arstechnica.com
arstechnica.com
There's more going on here than just MCAS and angle of attack sensors though. From the KNKT preliminary report:
At 23:31:09 UTC, the LNI610 PIC advised the ARR controller that the altitude of the aircraft could not be determined due to all aircraft instruments indicating different altitudes.
Crash happens 45s later. (More correctly, the FDR stops recording.)
From the same report, four separate maintenance records containing one or more defects in: indicated airspeed, indicated altitude, speed trim fail, mach trim fail. These were reported by multiple crew, repaired by maintenance per manufacturer procedure, and tested, and error state cleared.
The stick shaker was active for all of Lion Air 34 and most of 610. That is not an airworthy aircraft, and the preliminary report states this.
Obviously something does not pass the smell test. Either there's a very serious problem with the prescribed repair and verification procedure. Or there's a very serious crime if the claimed repairs and/or verification are inauthentic. Both seem incredible to me.
Common to airspeed and altimeter is the static system.
But as a pilot what really gets my attention, and not in a good way, is that apparently automation is confused, detecting multiple current sensor disagreements and flags, and yet it's still taking action.
I still don’t understand why altitude wasn’t considered - surely stalling speed close to the ground would result in less damage than pitching towards the ground an accelerating?
And how much can those sensors possibly cost anyway? (Real question - I have no sense if we’re talking a few dollars, a few thousand, few million, or what)
The optional warning they're talking about is just a light in a random section of the cockpit called "AOA disagree". That's it. It can't help the Lion Air crew, because the world wasn't aware that AoA was hooked up to a control surface through a new system called MCAS. And it's not in the central EICAS error display, so it's not where the pilots are supposed to be looking for information to help them diagnose an emergency. And it doesn't explain anything about why it might be super bad that there's an AoA disagreement.
So even if you know that MCAS exists and could malfunction, you'd have to also know that it uses AoA internally. Basically, the light only helps you if you already know both what MCAS is and how it works, and at that point you probably weren't going to be crashing anyway?
The correct information in the cockpit to use to help with the problem is what the Lion Air crew did the day before the crash: get a stall warning, see and hear that the trim wheels keep moving, notice that the yoke feels heavy, and move to the memory item for runaway trim.
I really wish we (the public) could stop hyperventilating and let the investigators investigate. When they finish, we can work on making the necessary changes. Aviation has a remarkably effective safety culture. That doesn’t get many clicks though.
It’s an optional extra so I suspect that one led was being charged at an absurd rate, because it was actually necessary.
The flight crew the day before had to hunt through manuals as well, and I haven’t seen any indication anywhere that suggested that the problem persisted for that entire flight - which could easily be the case if you tie a pilot overriding flight control system to a single sensor. Further I’d question a flight control system that pushes the nose down apparently without considering altitude
> It’s an optional extra so I suspect that one led was being charged at an absurd rate
The optional extra is actually an AoA visual display, and the light just comes along for the ride with the display. It's letting you know that you can't rely on the AoA display. It's not trying to communicate danger or emergency. That's not its job. There's already a system called EICAS for the plane to communicate urgent errors to the pilots, and that's where pilots look.
> because it was actually necessary
It really really wasn't. That light should not be used by pilots to diagnose anything. We don't want pilots to have to know how the airplane's internal systems were built. The MCAS system ultimately performs trim operations. We want pilots to notice trim aberrations, which have many possible causes (including purely mechanical ones!), and know how to disable the trim motor if the automatic trim is malfunctioning. If they can do that, they can solve many more problems than just MCAS. And if they can't do that, their plane will nosedive from many more causes than just MCAS.
> I haven’t seen any indication anywhere that suggested that the problem persisted for that entire flight
As I understand it, it didn't persist on the flight the day before because the third pilot correctly noticed that the trim was misbehaving and performed the STAB TRIM CUTOUT that disables the motor, as trained. If the motor hadn't been disabled, MCAS would have continued to use it to mistrim.
> I’d question a flight control system that pushes the nose down apparently without considering altitude
Why? Wing stalls are the most common cause of aviation fatalities. They usually happen during takeoff or landing, at less than 1000ft. If they happened at altitude they wouldn't be fatal because you have time to recover from them.
If one is building a system to try to prevent wing stalls -- and one should because it's the lowest hanging fruit for reducing the fatality rate of aviation -- that system should absolutely operate at low altitudes when you're in the critical period of a stall being effectively unrecoverable once a spin starts, because it takes a minimum of hundreds of feet to recover. That's the time when the system matters most.