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

DaveReidUK 9th Jan 2021 21:16


Originally Posted by 2dPilot (Post 10964350)
Speed and Altitude from FR24 granular data

Thanks for that. It illustrates my earlier comment:


Originally Posted by DaveReidUK (Post 10964332)
Watch out for dodgy timestamps and latency issues.

The momentary climbs during the descent from FL110 and the equally abrupt variations in groundspeed are artifacts as a result of timing issues: ADS-B data isn't timestamped at source, so FR24's timestamps simply record when it arrived at their servers from the various enthusiast feeds regardless of latency.

So the altitude and speed point values on the charts (and also on my earlier chart) are correct, but not all shown at the correct point in time.

vanHorck 9th Jan 2021 21:22

I have a question: What would cause the speed to drop for half the descent before the speed drastically increased. Does this show a level of control after the initial problem?

ManaAdaSystem 9th Jan 2021 21:31

DaveReidUK

How many enthusiast feeds is available off the coast of Java? This is why I have a problem with FR24. It is treated as the truth even if is «recording» events in the middle of an ocean with no feeds available anywhere. People simply have no idea how it works, or what it takes to get reliable information from it.

waito 9th Jan 2021 21:33


Originally Posted by 2dPilot (Post 10964350)
Speed and Altitude from FR24 granular data

Thanks, I am fighting with Excel as well.
DaveReidUK is right with the uneven distribution over time. But still we can see that the Groundspeed is not one or two glitchy datapoints but somehow a continuous increase in the last 7 seconds (speed stops to decrease at 5600ft, starts to increase again at ~3000ft)
Why is the question. GS surely is calculated. From INS? What happened to the sources for INS? Was 735 retrofitted with GPS anyway?

I'm also (and always) sceptical with FR24 collected data, you have a first but somehow fuzzy picture.
Only the ALT drop seems to be realistic. that's "impressive" unfortunately.
I don't read more from it at this time.

waito 9th Jan 2021 21:45

Another thought: That 2nd Gen of 737 is mostly gone in the regions where people worry the most about individual safety, and it's a lower count compared to the more modern generations. So there shouldn't be too many hysteric people afraid of setting a foot in that type. If this accident was related to this type at all of course. The issue will be found I believe, changes will be recommended in time. Just no need to be hysterical.

ManaAdaSystem 9th Jan 2021 21:56

The rudder issue is a dead end. Fixed a long time ago.
This is a loss of control accident. Why is anyones guess. We have had high speed loss of aircraft due to weather, disorientation, loss of instruments, fatal control problems, icing, suicide, computer resets and so on.
No pilots will start an emergency descent because of decompression from 11000 ft, and if you have a fire you don’t point the nose straight down.
My money is on instruments or possibly an explosion that cuts control of the tail. Pure speculation, but that is the only thing we can do at the moment.

pattern_is_full 9th Jan 2021 22:13

"The only thing funnier than watching non-professionals trying to investigate an air accident, is watching dogs on youtube trying to chew toffee."

About the only things we know so far is that this aircraft 1) made a more or less ballistic dive into the ocean from about 11,000 feet, and 2) it appears to have done so in substantially one piece, which tends to rule out a major explosion.

And secondarily that there appears to be no communication. Although that is quite common - pilots try to save their lives by flying, not by telling ATC where to find the hole in the water (or ground).

That does not rule out (or in) a smaller explosion (accidental or intentional - no evidence yet), that perhaps disrupted hydraulic or control runs, or the cockpit floor, or the trim jackscrew - or something completely different. Not large enough to disassemble the airframe, but possible enough to render the controls inoperable.

There appear to be eye (or ear) witness reports of explosions (but read up on the reliability of eyewitnesses - it also make funny/sad reading).

But in any case, that is just one of many possible scenarios. Each one of which should rate an initial probability of 1% - until further evidence rules them out completely (probability = 0%) or does not. In which case they remain in the mix for continued consideration.

FlightDetent 9th Jan 2021 22:27


Originally Posted by TFE731 (Post 10964082)
Yes:
Gulf Air 072: A disorientated pilot dived into the sea with forward pressure on the side stick.
Air France 447: A disorientated pilot maintained back pressure on the stick until a stalled aircraft crashed into the sea.

In both these incidents having the two sticks physically connected together could have prevented both of these.

Not in the GulfAir case, if we're honest about the root cause. On the other side, Armavia 967 does belong on the list.

The only relevance the "boeing" label has is circumstantial. Since they have been producing aircraft longer than Airbus and their older models are less efficient. many fine aircraft are operated be companies and people who chose not to pay for something better. A little money only gets you to certain lengths, which will apply in all aspects of the operation.

The statistics of out-of-production AB are the same as BA. More importantly, creating statistics and comparisons on single (digit) data points is meaningless.

And long may it stay that fatal aviation accidents are rare, too few for statistical processing.

visibility3miles 9th Jan 2021 22:43

I read that takeoff was delayed by 40 to 90 minutes due to weather concerns. I do not have a link.

DaveReidUK 9th Jan 2021 23:05


Originally Posted by ManaAdaSystem (Post 10964369)
How many enthusiast feeds is available off the coast of Java? This is why I have a problem with FR24. It is treated as the truth even if is «recording» events in the middle of an ocean with no feeds available anywhere. People simply have no idea how it works, or what it takes to get reliable information from it.

That's a fair point about events in the middle of the ocean, but this flight went down less than 20 miles from a city of 10 million people, so we shouldn't be surprised if it was being tracked by several FR24 feeds.


Originally Posted by waito (Post 10964370)
Why is the question. GS surely is calculated. From INS? What happened to the sources for INS? Was 735 retrofitted with GPS anyway?

While it's true that some B735s are still flying around with inertially-sourced ADS-B, it's pretty clear from looking at previous tracks for the aircraft in question that it had GPS.

Groundspeed is indeed calculated by the receiving station from N-S and E-W velocity components, which are what the aircraft transmits. Those, of course, are also what is used to derive true track. As a general rule, if the track timeseries looks consistent (which it does in this case once the time jitters are corrected) then the groundspeeds are also likely to be correct.


jcjeant 9th Jan 2021 23:11

Hi,
Fishermen overflown by plane on takeoff talk about two explosions

waito 9th Jan 2021 23:26

Ok, I averaged per second, also to get rid of the stretch of diagram-time when many values per second. I know it's still not perfect. I also removed datasets with no_position=N

https://cimg7.ibsrv.net/gimg/pprune....566423ccab.jpg

You can see that the ALT drop does not flatten out at the end. Nor is it ballistic after 07:40:17 UTC.
Somebody mentioned stallspeed warning at 4000ft. Don't forget, to deduct IAS from Groundspeed, and Stall from IAS is impossible to guess. And in case the plane nose dived, you have variable GS over descend angle. Forget the Speed. Only the GS increase at the end is somehow a mystery.

krismiler 9th Jan 2021 23:34

We need to be sceptical of a witnesses statement such as this, people often see things such as fire or breakups which are later on proven not to have occurred.

If the wreckage is in 15m of water at a known location then the recovery should be fairly quick.

PoppaJo 10th Jan 2021 01:15


Originally Posted by jcjeant (Post 10964419)
Hi,
Fishermen overflown by plane on takeoff talk about two explosions

Fishermen always come out with these claims when these things occur in Asia but none have yet to feature in any report. Remember the dozens and dozens of fishermen eyewitness claims around MH370? A lot of time was wasted investigating these false claims.

camel 10th Jan 2021 01:17

CB's around here can become very big and nasty fast ....let you know if i hear anymore.

George Glass 10th Jan 2021 01:43

Indonesia.......

Wet season with big nasty thunderstorms........

Low cost carrier.........

I think we’ve been here before.

Despite all the BS spouted about the B737 it is still one of the most reliable aircraft ever built.
I have thousands of hours on them.
I have also operated extensively in Indonesia.
It wont be the aircraft.

wheels_down 10th Jan 2021 01:49


Originally Posted by vanHorck (Post 10964364)
I have a question: What would cause the speed to drop for half the descent before the speed drastically increased. Does this show a level of control after the initial problem?

Seems to be the head scratcher for many. This could have been the point they exited a cell.

Speed seems good right up until the second the altitude heads south. Speed seems pretty accurate during climb also, data seems good so far.

Disorientation I would still not expect initially anyway, such a instantaneous fall away from a level. Loss of control entering a severe CB, I most certainly would.

Really need to know either, what they flew into, or what the engineering history is. Certainly whatever occurred, to drop like that, on the engineering front, Tail or Rear Stab something has gone wrong (or fell off as mentioned above).

PJ2 10th Jan 2021 02:28

krismiler

Hmm...if 15m of water, that is exactly half the fuselage length, so the wreckage would be buried deeply if the descent was as fast as it appears, making recovery a bit more difficult. But it’s been done successfully before....

FlexibleResponse 10th Jan 2021 03:31

Blocked Pitot-Static System?
 
Compare the FR24 data stream of accident flight with previous departure of PK-CLC and same track from RWY 25R(?) CGK two sectors back.

On accident flight, the FR24 Groundspeed readout is 20-40 knots slower during climb from 4000 to 8000 feet.
On accident flight, the FR24 Groundspeed readout "freezes" just above 280 knots climbing above about 10,000 feet instead of increasing as per previous departure CGK two sectors back.

Blocked Pitot-Static System is a possibility?

katekebo 10th Jan 2021 04:23

I'm not a pilot and I apologize for intruding in a professional pilot forum.
Just thinking "Occam's razor" ...
Could this be just a case of a botched stall recovery? We don't know what could have cause a stall (pilot's error, unreliable IAS reading due to obstructed pitot tube, weather). But then, the pilot didn't apply proper stall recovery technique, resulting in loss of both speed and altitude, and by the time he pushed the nose down to regain speed it was too late (not enough altitude) and basically flew the airplane into the water. This would be consistent with the GS and ALT plot, wouldn't it?


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