Another 737 MAX-8 down

a reply to: RadioRobert

Anyway, the new info points to something more significant at play than simply wrestling the MCAS IF they had issues while it was deactivated.

Maybe the delay in the release of the update points toward that potential issue.

originally posted by: JIMC5499
a reply to: KansasGirl

I've never heard of this reporting system and I've been around aviation for all of my adult life. In 80's and 90's I worked towards being an air crash investigator. I know that Boeing has a reporting system and the airlines are required to report certain things to the FAA, but, I've never heard of reporting to NASA.

ASRS has been around for a long time. It started as a "fess up and get out of jail free" program. If you run into an unsafe situation, even if you caused the situation, you can file what we call a NASA form and, except in some situations (crash, intentional act, etc.) you can avoid any sanction for a violation of regulations. You have to file the report before an enforcement action is started. NASA only acts as a validator for filing and dissemination.

According to the latest report, the aircraft suffered an impact that damaged the AoA sensor on takeoff. MCAS engaged, and the pilots followed the procedure to deactivate the system. After the system was disengaged, the crew manually trimmed the aircraft to bring the nose up, then restored power to the stabilizer, reactivating MCAS.

abcnews.go.com...

Officials say there was no evidence of a bird strike, and the crew followed proper procedures for troubleshooting an MCAS problem, until they turned the system back on. There's no word on how many times they turned the system off and on, although four times was mentioned. Officials are still attempting to determine why they turned it back on.

www.cbsnews.com...

a reply to: Zaphod58

So it wasn't a bird that impacted them but something else? Or that there was NOT an impact that damaged the sensor?

a reply to: KansasGirl

They're still attempting to determine that. The final report will take about a year. They said there was no evidence of a bird strike, but then mention the engines, not the AoA sensor.

Reading the full report, there was something weird going on with the aircraft that wasn't just MCAS.

The Executive Summary reads:

On March 10, 2019, at 05:38 UTC, Ethiopian Airlines flight 302, Boeing 737-8(MAX), ET-AVJ, took off from Addis Ababa Bole Int. Airport bound to Nairobi, Kenya Jomo Kenyatta Int. Airport. Shortly after takeoff, the Angle of Attack sensor recorded value became erroneous and the left stick shaker activated and remained active until near the end of the flight. In addition, the airspeed and altitude values from the left air data system began deviating from the corresponding right side values. Due to flight control problems, the Captain was unable to maintain the flight path and requested to return back to the departure airport. The crew lost control of the aircraft which crashed at 5: 44 UTC 28 NM South East of Addis Ababa near Ejere village.

There were multiple warnings sounding, beginning with an Anti Ice warning, ending with an overspeed warning until impact. The left side stick shaker was active the entire flight and the AoA indicator on the left side read a maximum of 75 degrees.

Full report can be found here:

www.flightradar24.com...

a reply to: Zaphod58

The AOA sensors were all over the place. Why am I thinking counterfeit or defective sensors?

a reply to: JIMC5499

Yeah, that's what I'm starting to think too. Those sensors are pretty damn bulletproof normally. To have two, on the same type, go bad this close together is pretty telling.

This part stood out too.

At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.

That's similar to JT610. I wonder if they have a bad batch of computers too.

Airspeed readings being different wouldn't be surprising as the flight computers will determine the data unreliable once it thinks you are above a specific angle of attack because the airflow over the pitot is disrupted.

The other stuff I am not sure how inter-related it is, but it is odd either way.

According to a report I just saw, the 737 Classic could undergo a situation where the crew could have trouble adjusting the stabilizer using the natural trim wheel. Pilots were apparently warned that when the stabilizer was in the nose down position, with the crew pulling the column full back, into a nose up position, similar to what was seen here, the manual trim would have trouble correcting because of the opposing forces. Pilots of the NG and Max say the manual makes no mention of that possibility.

originally posted by: Zaphod58
Officials say there was no evidence of a bird strike, and the crew followed proper procedures for troubleshooting an MCAS problem, until they turned the system back on. There's no word on how many times they turned the system off and on, although four times was mentioned. Officials are still attempting to determine why they turned it back on.

www.cbsnews.com...

Let me make a W. A. G. (Wild A.. Guess) from a pilot's perspective why they would have reset the stab trim switches (there are 2 under a guard on the console between the pilot. The erroneous AoA triggered the MCAS and it ran the stab trim to 2.6 degrees nose down. Somebody recognized the problem and turned the stab trim motors off. But then they are in a steep dive picking up a ton of speed. High speed moves the aerodynamic center of lift aft which pitches the nose down even more. They are pulling on the yoke with all their strength, but with all that speed, the elevator forces would be enormous. To reduce elevator force they need to manually trim the nose up. But they turned off the stab trim switches so the manual trim button on the yoke would not work. So to get them working they turn the switches back on. OH! (bad word!) MCAS resets, reactivates and makes things worse.That is only a guess but the CVR might confirm it. One question I have is whether this aircraft had a stab trim override switch, which on some 737s can prevent the manual trim yoke button and manual trim wheel from overriding the autopilot/software imposed inputs.

a reply to: F4guy

One of several articles I read said basically the same, that they turned it back on to get trim control back.

originally posted by: JIMC5499
a reply to: Zaphod58

The AOA sensors were all over the place. Why am I thinking counterfeit or defective sensors?

Since the sensors are apparently dependent on airflow, could it be possible that aerodynamic deficiencies or erratic wind conditions could cause the problem?

a reply to: ausername

It only affected the left side on both aircraft. So either they were sending bad data to the computer, or the computer was bad and reading it wrong.

originally posted by: ausername

originally posted by: JIMC5499
a reply to: Zaphod58

The AOA sensors were all over the place. Why am I thinking counterfeit or defective sensors?

Since the sensors are apparently dependent on airflow, could it be possible that aerodynamic deficiencies or erratic wind conditions flat or nose high attitudecould cause the problem?

Not really.The only attitude that cause cause such a high AoA would be a deep stall, which would be accompanied by a flat or nose high attitude. And that (deep stall) usually only occurs T-tail aircraft like the MD-80 or some Antonov aircraft. The airspeed numbers don't show any erratic wind conditions.

accumulation of bad design concepts, looks like. don't know if boeing have any pilots in their design team
a reply to: F4guy

originally posted by: JIMC5499
The AOA sensors were all over the place. Why am I thinking counterfeit or defective sensors?

I wonder how far the inlet vortex can reach under certain conditions: powersetting, airspeed, air density, due point, wind, etc etc etc etc. I can only find data from an aircraft simulated sitting on the tarmac with split vortexes, i wonder how powerful a single vortex that has become attached to the airplane body could become and how far forward it can reach.

So, with the new more powerful engines that had to be mounted more forward and up (closer to the AoA sensor), could the inlet vortex reach all the way to the AoA sensor at certain extreme conditions, i doubt it but, yeah

a reply to: JesperA

Interesting theory!

I've seen them on the ground lots of times (usually when it's raining or snowing), especially on the 737's and the A319's. And they definitely move all over the place due to varying conditions (wind, nearby fixed objects, terrain variations, etc.). Though, I wouldn't think at speed they would reach very far if at all. However, your idea is interesting in the context of how a sensor might get damaged, on or near the ground.

ETA - Boy, wouldn't that be a son of a gun to try to mock up for testing!!!