737-500 Down in Indonesia?

Something sure slowed them down quick like that! They burned off some airspeed quick, and how!

That, or they pitched up dramatically just before the stall.

The aircraft was stored for 9 months last year. It had flown just under three weeks since coming back from storage, and underwent a required engine corrosion inspection December 2.

www.wsj.com...

a reply to: Zaphod58

I'm just guessing, but presumably it was stored due to cutting back on someone's fleet due to lack of travelers/demand in 2020?

I wonder how common this type of storage is among carriers, and what you think about the risk it might introduce to a plane (moisture buildup? losing track of periodic maintenance/replacements?).

Is this something that you could see becoming a problem if/when air travel starts to bounce back?

a reply to: SleeperHasAwakened

Just about every carrier parked large portions of fleets. I don't see something like this happening more, but more diversions and emergency landings for a little while. We already saw an Air Canada 737 Max divert to Tucson after coming out of storage for almost two years.

To give you an idea, I've got pictures of multiple American 787-9 and 777 airframes that are being used SFO-DFW and LAX-IAH.

Did they check the pitot tubes for insect nests?

a reply to: Blackfinger

Unlikely. It flew for several weeks before the accident.

The engine inspection was for a July 2020 AD requiring inspections of the bleed air fifth stage check valve for corrosion after long term storage. If the valve opened normally at take off power, it could fail open when power was reduced after the climb. That would result in an unrecoverable compressor stall, and engine that can't be restarted in flight.

aviationweek.com...

Data has been extracted from the FDR. The CVR case has been found, but the search continues for the memory unit. Both engines were operating at impact. A preliminary report is due within 30 days.

Two days prior to the crash, another crew wrote up an issue with the autothrottle on the aircraft, but apparently it wasn't written up properly. Investigators don't know exactly what the issue was because of that, but the previous crew deactivated the autothrottle and continued the flight.

mentourpilot.com...

The flight control computer, autothrottle computer, and autothrottle actuator assembly are being analyzed. The pilots change the autopilot from using the pre-programmed "strategic mode" to "tactical mode". Afterwards the aircraft began a gradual left turn and the descent to impact. Twenty seven hours of data has been extracted, covering 18 flights. The pilots had flown 142 hours and 113 hours over the previous 90 days.

www.flightglobal.com...

a reply to: Zaphod58
Zaph I think you and I may have discussed this elsewhere recently, but for those that dont know I'll explain a little more. I have done a bunch of these inspections myself and its quite quick and easy. There are actually two separate but related types of inspection under an AD. The first is a general one that involves function checking both the 5th stage check valve and the Pressure Reduction/Shutoff Valve(PRSOV). You open the left hand cowls of the engine and using a 7/16" or 3/8"(I forget which exactly) ring spanner, manually cycle the valve from the external shaft extension 3 times. The valve must return to its default position smoothly, quickly and without any undue shuddering or noise. If it doesn't then further troubleshooting may be required and/or the valve replaced. This is a quick and simple inspection taking no more than 2-3 minutes and from cowls open to close it should be less than 10 minutes.

The second inspection is a detailed inspection of the 5th stage valve only. But again because the 737 CFM is so "quaint" in size its a doddle compared to big motors. In this AD inspection you need to gain access to the core again and remove the upper and lower valve clamps, carefully pull out the valve, preferably without munting the "E" seals and inspect the valve on a bench. There are pictures attached to the AD showing what you are looking for which is basically bad corrosion on the valve's butterfly shaft, valve body and valve flaps. You are also required to do an end free play check to ensure the valve flaps aren't banging around which can cause cracking that leads to failures. In my experience virtually all valves show some signs of corrosion that would be considered normal. I haven't personally seen a badly corroded one yet but I know one or two have been picked up in our fleet. If you have a positive finding you need to replace the valve.

Was this a contributing factor in the Lion Air 735 crash? I dont know. But what it does highlight is that a lot of aircraft have been stored and problems are being found. If your maintenance teams aren't being careful, something big could slip through that could lead to a fatal accident. Now is most definitely not the time for airlines to penny pinch or get complacent, but they probably will.

According to the preliminary report, the autothrottle was written up as unserviceable on Jan 3rd. The electrical contacts were cleaned, and a BITE test showed good. It was written up again on the 4th, and this time, failed testing after cleaning the contacts again. On the 5th, the TO/GA contacts were cleaned and the test passed.

Passing through 8150 feet, the left throttle was reduced while the right remained at the same setting.

a reply to: Zaphod58

Sounds like another case of push button aviators failing to fly the aircraft. I have seen guys keep pushing a button instead of taking manual control..

Full preliminary report.

a reply to: 727Sky

It sounds like a combination of mechanics that didn't want to do too much work, and push button aviators. They should have noticed the throttle moving with the left engine pulling back, as well as the N1 decreasing on the left engine.

The CVR memory module has been found and recovered.

The CVR has been downloaded, and contains "good data". According to investigators, they recovered 4 channels of audio. It contains 2 hours of recordings that now have to be synchronized and analyzed.

www.usnews.com...

Update by the investigators, is that CVR channel 4 was disrupted, but added data to the investigation. The other three channels were intact.

The crew failed to properly monitor a faulty auto throttle system. It had been written up over 65 times since 2013, and was still not working properly at the time of the accident. As the aircraft passed through 8,150 feet, after being cleared to 29,000 feet, the left throttle started reducing power. The right throttle remained at its set position. They were instructed to stop their climb at 11,000 feet for traffic avoidance. As they passed through 10, 600 feet, the FDR recorded them in a left turn. They reached 10,900 feet, where the FDR recorded them on a heading of 016, with a pitch up of 4.5 degrees, and rolled left 45 degrees. The left engine throttle continued decreasing, while the right remained at power. The auto throttle disconnected 20 seconds before the FDR stopped recording, with a nose down of more than 10 degrees.

The first officer said "Upset. Upset." and "Captain. Captain." before the CVR stopped, but the Captain's channel wasn't recording. KNKT had raised the issue of lack of upset training after the 2014 crash of an AirAsia Indonesia aircraft, but it wasn't implemented. According to the report, upset and recovery training will now be required.

www.aljazeera.com...