Several hurt as PIA plane hits air pocket

FULLTHRUST · Post by **FULLTHRUST** » Wed Nov 22, 2006 5:34 pm

Quote:
This is a coverup by PIA. The chairman was in touch with the Pilot, and instructed him to maintain the air pocket story. The truth is that the Auto pilot misbehaved and the pilots were a litle slow in reacting.

Could you please elaborate?

Still awaiting....on auto pilot!!!!!!!

cheetah · Post by **cheetah** » Wed Nov 22, 2006 6:05 pm

I am not a pilot.. do not have the technical know how. However, thats the real cause! you want more info, talk to one.

FULLTHRUST · Post by **FULLTHRUST** » Wed Nov 22, 2006 7:13 pm

I personally feel that the REAL CAUSE is NOT the auto pilot, but the PILOT.

The aircraft went back to KHI on same auto pilot system.

The operation check on both AP1 and AP2 were satisfatory and NORMAL on both CWS and CMD modes, done at ISB.

However, flight data recorder and cockpit voice recorder have been removed from the aircraft for further investigations.

FULLTHRUST · Post by **FULLTHRUST** » Thu Nov 23, 2006 12:02 am

Had it been an AUTO PILOT MISBEHAVIOUR, crew would definitely reported that in the log book, however they did not.

Who covered whom? I dont know!!!

Adnaan786 · Post by **Adnaan786** » Thu Nov 23, 2006 9:56 am

It's not unusual for things to happen in the air, but when they're checked on the ground they work fine.

In such instances the engineers usually tell the pilots that the next time this happens, have a look at this, this and this, and tell us what you find - and then the engineers are usually able to trace the problem.

I have a question: I'm not familiar with the A310 auto pilot system, but isn't it the case in modern aircraft that if an ambiguity occurs in the system that it disconnects automatically, and when it disconnects the aircraft is already in trim and there is a clear aural warning, so you shouldn't really lose 1000ft due to that happening. If on the other hand the autopilot didn't disconnect and took a mind of it's own, and the pilots had to disconnect it manually then that is a pretty serious issue.

If anyone has anymore info on what happened I would be interested to know.

AM · Post by AM » Thu Nov 23, 2006 11:42 am

AT 1222 GMT flying at 27727 feet autopilot B in CMD the aircraft apparently came under a down draft CAT and pilot lifted the nose .speed was reduced .Vertical acceleration -6 . It took 50 seconds for recovery .The autopilot /autothrottle system did what it was supposed to do ,FULL THRUST (:) (fullthrust do you read) .Pilots disengaged auto pilot (Manual disengagement). The aircraft recovered from descent ,engine overboost for 5 seconds and speed recovered.Pilots followed flight plan maintained 12000 feet .At isb all checks of system satisfactory.CVR DFDR transcribed and readout carried out at PIA facility .Aircraft ferry flown to KHI to preclude any system fault and detailed testing.Test flight on 23rd at 1200hrs GMT.Investigtion being carried out by SIB.

Adnaan786 · Post by **Adnaan786** » Thu Nov 23, 2006 2:43 pm

Thank you AM. There are a few things I don't understand though. I hope you can clarify them.

...Vertical acceleration -6. It took 50 seconds for recovery

What does -6 mean?

So in 50 seconds the aircraft lost 15000ft? WOW!

The autopilot /autothrottle system did what it was supposed to do ,FULL THRUST...

Why was this? Did the aircraft stall?

...autopilot B in CMD the aircraft apparently came under a down draft CAT and pilot lifted the nose

Is the pilot able to manoeuvre the aircraft whilst autopilot is engaged?

Thank you.

FULLTHRUST · Post by **FULLTHRUST** » Thu Nov 23, 2006 3:46 pm

Roger copied AM

But I have to say something here;

A) Vertical Acceleration is known as "g", and value of -6 means a lot. Could have broken the fuselage in the air. If it is vertical speed of -6000 ft/min, that is quite understandable.

B) It could be a possible CAT (clear air turbulence), and as you said the crew lifted the nose first and then after a while they disengaged the AP and AT which is quite opposite to what is described in Flight Crew Operating Manuals.

CAUTION

As per FCOM Bulletin No. 05/02 Page 11;

DO NOT ATTEMPT TO MODIFY A/C FLIGHT PATH ACTING ON CONTROLS, IF AP IS NOT DISCONNECTED.

I think the vertical speed was -6000 ft/min, and the reports are of 5000-6000' of descent.

There is no readout facility at ISB, that is only at KHI. They removed DFDR and CVR at ISB.

SIB people..............what would they do.......there is no rated pilot in SIB.

Is the pilot able to manoeuvre the aircraft whilst autopilot is engaged?

No they are not supposed to do that, first they have to disconnect the AP and then act on controls.

With AP in CMD if the pilot counteracts the AP (elevator order), the AP will move the THS (autotrim order) so as to maintain the aircraft on the scheduled flight path. THS is trimmable horizontal stablizer.

Also, the autopilot override does not cancel the AP autotrim orders.[/quote]

cheetah · Post by **cheetah** » Thu Nov 23, 2006 4:19 pm

thats the issue, many try to fight the autopilot. A very common exercise in the airbus simulator.

FULLTHRUST · Post by **FULLTHRUST** » Thu Nov 23, 2006 4:20 pm

I have observed an acute emergency while going to Quetta from ISB, and it was AP-BEG, climbing with a vertical speed of 4300'/Min, over Hangu, a PIA 747 inbound to ISB, descending, all the TCAS advisories were there in the 310 cockpit. What the Capt. did was disconnected AP and AT at once, reduced the thrust manually, and levelled off the aircraft. That was a near miss by a few hundred feet vertically. I saw the big bird right overhead.

The presence of mind and to do it right is the key. I can only say the heart comes to throat in such situations.

AM · Post by AM » Fri Nov 24, 2006 5:01 am

Thanks for the comments both Fullthrust and Adnaan.As for the queries ,first of all there was a confusion created by -6 and it was a mistake and so in 50 seconds the aircraft did not lose 15000ft .50 seconds was for recovery from dive and removal of VMO warning which came on when speed was increased. - 6 was actually the Angle of attack.It is not g as the fuselage would not bear such stress.Thanks for pointing it out .The aircraft had passed its FMC TOD (Top of descent )and had a speed of 204.3 Kts when apparently came under CAT and the speed dropped to 111.3 KTS .This speed drop is also because crew pulled up the aircraft.No stick shaker was activated and stall condition was not there but autothrottle FAC commands fullthrust.The pitch angle was -2.8 which came to -3.7 due FMC (descent) and when in CAT went to -18 (max) during the whole episode.The normal angle of attack was 2.6 which reached -6.3 at dive.Its very true that with AP in CMD if the pilot counteracts the AP (elevator order), the AP will move the THS (autotrim order) so as to maintain the aircraft on the scheduled flight path and the autopilot override does not cancel the AP autotrim orders.

I myself have felt such a rapid descent once in windshear on a 737 while landing at pasni and once on a 310 when something similar happened all crew members were discussing how to unload the furniture brought from bieging when suddenly came under CAT ,rapid descent,pull on the column ,but in that case we depended on the autothrottle to take care .FAC A/T took over and gave fullthrust and recovered. As fullthrust put it The presence of mind and to do it right is the key and the heart comes to throat in such situations.But in that case back in lounge all praise was for the autopilot system .

DFDR / CVR transcribing facility is only at Karachi in PIA engineering .Data can be downloaded anywhere now as Digital medium is used and can even be sent secure and electronically. In this case however both boxes were sent to Karachi and transcribed in the night.Test flight not carried out as all airframe structure and avionics checks are beingdone and airbus is also been brought in picture for thier comments and advice.

FULLTHRUST · Post by **FULLTHRUST** » Fri Nov 24, 2006 2:23 pm

Thanks very much AM to bring up the facts;

I would only say, STAB TRIM (Pitch Angle) of -18 means crew were fighting with the controls and the AP AutoTrim orders made it to -18, and thats the limit of going opposite to the manual inputs by the crew. That

would have been a killer.

Allah ka Shukar hay!!!!

For those who are interested in knowing an other disaster recovery please visit http://www.tsb.gc.ca/en/reports/air/199 ... 5h0004.asp

Max · Post by **Max** » Fri Nov 24, 2006 2:52 pm

Most of our passengers treat the seat belt as an insult not just on PIA but also on other Middle East carriers.

FULLTHRUST · Post by **FULLTHRUST** » Fri Dec 01, 2006 6:57 pm

AP-BDZ has been GROUNDED by AIRBUS INDUSTRIE till further notice. It might be WRITTEN OFF.

It was done after having the DFDR read-outs.

Abbas Ali · Post by **Abbas Ali** » Fri Dec 01, 2006 7:08 pm

Did AP-BDZ suffer damage to its structure/fuselage in this incident?

Abbas