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-   -   737-500 missing in Indonesia (https://www.pprune.org/rumours-news/637944-737-500-missing-indonesia.html)

physicus 10th Jan 2021 04:24

Here's a better plot with infrared satellite overlay. While they almost certainly were in IMC when the problem occurred, it doesn't look like they came close to significant CBs.


isky998 10th Jan 2021 04:45

My dad is an LAE. From the flight pattern recorded, he suspect that the check valve is corroded. Due to the fact that most of the aircraft are grounded due to COVID-19, virtually no maintenance was done on them to save cost.

Ngineer 10th Jan 2021 05:48

Regardless of what has happened here, one thing is for sure. There will be many rusty pilots, engineers and aircraft flying around soon if the world ever gets back to normal flying. And in a lean financial market. Be prepared for a few incidents.

jetstreamsjdlz 10th Jan 2021 06:04


Far from me to give any conclusion but: this is rainy season and also season of mud dauber wasps which are active in Indonesia. I have been working in JKT for some years. There are airlines who never put pitot probes covers for night stops.
And some parking stations are close to ditches where wasps can collect mud.
I have pictures of aircraft's fuselage fully covered by mud dauber wasps (not a sriwijaya aircraft), taken some years ago. Not only maintenance staff is not trained to recognize them and possible consequences but also they do not take any action for inspection - at least - when there is presence of mud dauber wasps in vicinity of an aircraft not having been protected.
All my attempts to convince maintenance staff installing pitot probes covers were useless, even after I contacted safety Dept. (not sriwijaya, again)

Once again, this is a general situation, I do not blame particularly Sriwijaya and do not say that this is what happened.

On top of it, an obstructed pitot (obstructed by wasp's nest) should be at least detected by the crew during take off run when comparing speed between CAPT and FO, unless both of them are obstructed.
Obstructed Pitot by wasp's nest is not necessarily something you can notice from the ground during the turn around of the aircraft.

procede 10th Jan 2021 06:06

My bet is on a ripped off vertical tail due to gusts / fatigue / rudder movement, as descending and decellerating like that indicates a very high drag (parachute like) configuration. Check AA 587. Maybe I'll try to calculate later what the drag coefficient must have been...

AfricanSkies 10th Jan 2021 06:44

Flexible response, no, groundspeed on FR24 doesn't depend on the actual aircraft's pitot static system. Groundspeed is groundspeed, not airspeed anyway.

For the PP's on here, how does this accident profile fit a deployed reverser in flight?

WatchTheSkies 10th Jan 2021 07:08

Originally Posted by AfricanSkies (Post 10964534)
For the PP's on here, how does this accident profile fit a deployed reverser in flight?

If the flight data is correct, Reverser Unlocked or severe damage to the left engine could be a possibility. The aircraft appeared to yaw to the left at an increasing rate until it entered the sea. Looks like when the autopilot finally gave up the aircraft yawed left and the nose pointed down. Airspeed must have increased, increasing the drag on the left engine causing yaw to accelerate. The engine being slightly below the C of G pulled the nose further down until the aircraft was inverted and then continued to pull the nose up relative to the horizon while inverted, causing the increase of lateral speed (GS). The yaw to the left continued while inverted causing the increasing heading until it entered the sea. This is just a guess based on the data.

Ollie Onion 10th Jan 2021 07:19

Let’s face it, being in Indonesia it could be anything, maintenance, training, pilot error are all strong trends in previous accidents. We won’t know until the investigation is done so let’s wait for that.

DaveReidUK 10th Jan 2021 07:54


Nicely graphed, though the rounded time values on the X-axis are a bit irregular.

At the risk of stating the obvious, while the ROD (fpm) remained more-or-less constant during the descent, the flight path angle wrt the ground must have become shallower towards the end of the dive (i.e. the aircraft was beginning to pull out), since FPA is simply the resultant of horizontal and vertical velocity.

For example:
At 4000' (07:40:22) V/S 40,000 fpm (395 kts); GS 120 kts -> FPA -73°
At 2000' (07:40:25) V/S 40,000 fpm (395 kts); GS 210 kts -> FPA -62°

All values approximate, but the difference is marked enough to accommodate any slight variation.

andryan 10th Jan 2021 08:07

The captain's wife was interviewed by the news website and said that he unusually apologized to her and their children. Coincidence or something siginficant related to the accident?

DaveReidUK 10th Jan 2021 08:40


I don't see how the data supports much, if any, of that scenario.

For a start, the aircraft descended in a RH spiral, not a LH one.

silverstrata 10th Jan 2021 08:49

Originally Posted by olster (Post 10964253)
Correct. The rudder hardover theory was a low speed event.

Yes, but the 737 also had at least one high-speed rudder hard-over event in the cruise.
Due to their speed this crew were able to recover, but it was a major event that nearly turned them upside-down. But if the crew were less able, or disorientated due IMC, or if there was an airframe failure due to these stresses, then a high-speed rudder hard-over could result in a plunge into the ocean.

brika 10th Jan 2021 09:29

When was the last time this plane actually flew in the air, before this?

wheels_down 10th Jan 2021 09:37


about 140 flights since its 6 month grounding.

Old Farang 10th Jan 2021 10:00

Indonesia locates black boxes after deadly plane crashIndonesia locates black boxes after deadly plane crash (bangkokpost.com)

"We have located the position of the black boxes, both of them," said Soerjanto Tjahjanto, head of Indonesia's transport safety agency.
"Divers will start looking for them now and hopefully it won't be long before we get them." A military vessel picked up the plane's signal, and divers recovered wreckage from around 23 metres below the water's surface, the transport ministry said Sunday, citing Indonesia's military chief Hadi Tjahjanto.

It did not specify if the signal was from the downed plane's voice and flight data recorder.

Owen61 10th Jan 2021 10:20

I have a genuine question about pitch control on 737s, maybe you would know?

The original 60s version had the low, thin, P&W engines.

The MAX has these large, forward CFM motors. These cause pitch-up under thrust and so necessitated the introduction of MCAS to fix it.

This model is the 2nd gen 500 from the 1980s, so it's too early for MCAS, I understand.

However, the 500 does have rather large CFM motors. It looks a lot like the MAX. So, presumably, it also had the pitch-up issue (though perhaps to a lesser extent than the MAX).

If so, my question is, what was done in the late 80s to mitigate the pitch-up tendency on the 500 series when it rolled out?

EIFFS 10th Jan 2021 10:41


the 500 has the shortest body, it’s tough as old boots, highly unlikely, the short body with the highest thrust engine options does make it a little more demanding engine out, but only at LOW SPEED at altitude this wouldn’t be an issue, this appears to be very rapid loss of control.

with regards to so called explosions reported by fishermen, could be thunder or sonic boom if it went down under power ballistically.

Only 15m of water so the front will be buried in the mud FDR should be on top

Easy Street 10th Jan 2021 10:47

Originally Posted by Owen61 (Post 10964684)
The MAX has these large, forward CFM motors. These cause pitch-up under thrust and so necessitated the introduction of MCAS to fix it.

Not a 737 expert so will leave the rest of your question for someone else to answer, but I do know enough to correct the misunderstanding above. MCAS has nothing to do with thrust-pitch coupling: it was introduced to address aerodynamic effects of the MAX’s LEAP engine pods, which are larger and mounted further forward than the CFMs. At high angle of attack, the airflow impinging on the under-surface of the pods induces a pitch-up moment which must be counteracted to meet certification requirements relating to stick force gradient. No doubt the CFMs are worse than the P&W in that regard: just not bad enough to need counteraction in the way the LEAPs do.

Back at NH 10th Jan 2021 11:01

The dauber wasp theory is unlikely as the aircraft was on a 1:30hr turnround prior to the accident flight.

A downdraft of the magnitude required to get the vertical speeds recorded from the FR24 data is most unlikely as how would they dissipate before the surface. The fishermen nearby didn’t report hurricane force winds.

EIFFS mentions fishermen hearing ‘explosions’ that he purports may have been a sonic boom. After COPA 201 had a loss of control due to VG failure at FL250, it exceeded the speed of sound before breaking up at FL100. With the Vertical speed assumed from the FR24 data and the ground speed also recorded from the same source at the later stages of the dive, it can’t have been far off.

WatchTheSkies 10th Jan 2021 11:09

Originally Posted by DaveReidUK (Post 10964599)

I don't see how the data supports much, if any, of that scenario.

For a start, the aircraft descended in a RH spiral, not a LH one.

Not sure which data you are referring to but i was using this one below

Originally Posted by F-MANU (Post 10964028)
FR24 ADS-B data
Timestamp Alt GS HDG
07:39:56Z 10800;287;42
07:40:02Z 10900;287;30
07:40:05Z 10900;287;23
07:40:08Z 10725;287;6
07:40:14Z 8950;224;339
07:40:16Z 8125;192;338
07:40:20Z 5400;115;11
07:40:27Z 250;358;93

042 to 030 in 6s = -2°/s
030 to 023 in 3s = -3.5°/s
023 to 006 in 3s = approx -6°/s ( approx -60ft/s)
006 to 339 in 6s = approx -5°/s ( approx -296ft/s)
339 to 338 in 2s = -0.5 °/s ( approx -413ft/s)
338 to 011 in 4s = approx +8°/s ( approx -681ft/s)
011 to 093 in 7s = approx +12°/s ( approx -736ft/s)

( when upright, heading reducing means left turn. Increasing means a right turn. Opposite direction when inverted, of course)
Initially there was a left yaw for 9 sec that became a nose dive. From the data you can see, when the aircraft pitched down, there was a huge forward acceleration vector which temporarily reduced the yaw vectors effect on the heading change. But as drag increases exponentially with velocity, the yaw vector caught up and increased the heading change again. The increase in lateral speed and direction of heading change is IMO best explained by the aircraft going inverted and the nose moving upwards relative to the horizon due to the exponentially increasing drag from the left engine

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