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BA B772: Severe Turbulence And Emergency Descent  
User currently offlineAirGabon From Switzerland, joined Dec 2003, 890 posts, RR: 2
Posted (4 years 11 months 1 week 6 days 5 hours ago) and read 19630 times:

Any information? Found on internet (no link, sorry):

"A British Airways Boeing 777-200, registration G-VIIR performing flight BA-2156 (dep. Oct 18th) from Antigua (Antigua and Barbuda) to London Gatwick,EN (UK), was enroute at FL390 overhead the Atlantic about 8 minutes ahead of their next waypoint N46 W30, when the crew reported severe turbulence and requested to descent. Oceanic control was unable to clear the airplane due to conflicting traffic at FL380, FL370 and FL360. The crew then advised, that they were executing oceanic contingency procedures and performing an emergency descent to FL350, the crew reporting they had the conflicting traffic on their TCAS screen. After the airplane had levelled at FL350, the flight was cleared to proceed on FL350 and reached London for a safe landing about 2:45 hours later about 15 minutes ahead of schedule. "

As AF445 GIG-CDG MayDay descent on 29th November due to severe turbulence.

21 replies: All unread, jump to last
 
User currently offlineJeffb77w From Dominican Republic, joined Dec 2009, 24 posts, RR: 0
Reply 1, posted (4 years 11 months 1 week 6 days 5 hours ago) and read 19485 times:

so they didnt get clear to descent.nice call by the pilot to do a emergency descent.

User currently offlineKaiarahi From Canada, joined Jul 2009, 3055 posts, RR: 28
Reply 2, posted (4 years 11 months 1 week 6 days 4 hours ago) and read 19296 times:



Quoting AirGabon (Thread starter):
so they didnt get clear to descent.nice call by the pilot to do a emergency descent

SOP - this is a common occurrence over NAT. Controller "can't" clear, descent at 90 degrees from track, controller clears at new FL.



Empty vessels make the most noise.
User currently offlineAABB777 From United States of America, joined Oct 2007, 588 posts, RR: 7
Reply 3, posted (4 years 11 months 1 week 6 days 1 hour ago) and read 18753 times:
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If BA2156 was not given clearance to descend, however they did anyway via emergency descent, how does this affect other a/c in the area (ie: conflicting traffic at FL380, FL370 and FL360)?

User currently offlineLMML 14/32 From Malta, joined Jan 2001, 2565 posts, RR: 6
Reply 4, posted (4 years 11 months 1 week 6 days 1 hour ago) and read 18508 times:



Quoting AABB777 (Reply 3):

The safety of the plane rests solely on the pilot. He had TCAS and he did it. Good thinking IMHO.


User currently offlineRobK From United Kingdom, joined Sep 2004, 3958 posts, RR: 18
Reply 5, posted (4 years 11 months 1 week 6 days ago) and read 18301 times:

Surely turning 90 degrees from track would quickly start to cause conflict problems with the aircraft flying on the adjacent track? The tracks are usually 10 degrees of latitude apart but I don't have a clue what that is in miles. I realise that there is no fixed distance as it depends where in the world you are, but what would be the approx miles between 46n30w and 47n30w for example, and how long would that flight have taken to start conflicting with the other traffic on the adjacent track?

R


User currently offlineAABB777 From United States of America, joined Oct 2007, 588 posts, RR: 7
Reply 6, posted (4 years 11 months 1 week 6 days ago) and read 18269 times:
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Quoting LMML 14/32 (Reply 4):
The safety of the plane rests solely on the pilot. He had TCAS and he did it. Good thinking IMHO.

Would local traffic around the BA flight also adjust their altitude, speed, etc to accomodate his emergency descent?


User currently offlineThrottleHold From South Africa, joined Jul 2006, 659 posts, RR: 1
Reply 7, posted (4 years 11 months 1 week 6 days ago) and read 18231 times:



Quoting RobK (Reply 5):
Surely turning 90 degrees from track would quickly start to cause conflict problems with the aircraft flying on the adjacent track? The tracks are usually 10 degrees of latitude apart but I don't have a clue what that is in miles. I realise that there is no fixed distance as it depends where in the world you are, but what would be the approx miles between 46n30w and 47n30w for example, and how long would that flight have taken to start conflicting with the other traffic on the adjacent track?

Tracks are seperated by 60nm laterally.
A 90 degree turn is initiated in order to establish on a track parallel and 15nm offset from the track centreline. Seperation with the adjacent track would then be 45nm.

Quoting AABB777 (Reply 6):
Would local traffic around the BA flight also adjust their altitude, speed, etc to accomodate his emergency descent?

No, they would continue on their original clearance as then everyone is aware of what each other are doing.


User currently offlineRobK From United Kingdom, joined Sep 2004, 3958 posts, RR: 18
Reply 8, posted (4 years 11 months 1 week 6 days ago) and read 18190 times:



Quoting ThrottleHold (Reply 7):
Tracks are seperated by 60nm laterally.
A 90 degree turn is initiated in order to establish on a track parallel and 15nm offset from the track centreline. Seperation with the adjacent track would then be 45nm.

Thanks, I didn't know that. I did of course mean 1 degree of lateral separation, not 10 !

R


User currently offlineBMI727 From United States of America, joined Feb 2009, 15810 posts, RR: 27
Reply 9, posted (4 years 11 months 1 week 5 days 19 hours ago) and read 16761 times:



Quoting RobK (Reply 5):
Surely turning 90 degrees from track would quickly start to cause conflict problems with the aircraft flying on the adjacent track?

No, this is the procedure for the NATS.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineLHR380 From , joined Dec 1969, posts, RR:
Reply 10, posted (4 years 11 months 1 week 5 days 19 hours ago) and read 16761 times:

This was discussed at the time it happened, cant recall the anet link though

User currently offlineLoalq From Switzerland, joined Jan 2007, 229 posts, RR: 3
Reply 11, posted (4 years 11 months 1 week 5 days 19 hours ago) and read 16595 times:

No mayday call needed for this "unauthorized" emergency descend?


"...this is your captain speaking. We have a small problem. All four engines have stopped."
User currently offlineBeansy57 From United Kingdom, joined Sep 2009, 8 posts, RR: 0
Reply 12, posted (4 years 11 months 1 week 5 days 19 hours ago) and read 16310 times:

ATC were unable to provide the desired descent clearance, the Captain believed his aircraft was experiencing such turbulence, he used his own authority to descend, however there are published contingency procedures on the North Atlantic Track system in place to allow you to do this, with a minimum of risk, when necessary.

Briefly, this involves turning left or right off your published NAT (the next nearest NAT will be 60 nm away) until you are 15 nm displaced, turning to parallel your original track, and only then descending to your desired altitude.

What we all have to remember is none of us were there dealing with it, also the pilots are trained to such a high standard, they would not perform a maneuver to endanger other aircraft.


User currently offlineZeke From Hong Kong, joined Dec 2006, 9210 posts, RR: 76
Reply 13, posted (4 years 11 months 1 week 5 days 18 hours ago) and read 15752 times:



Quoting AABB777 (Reply 6):
Would local traffic around the BA flight also adjust their altitude, speed, etc to accomodate his emergency descent?

ATC would endeavor to organize a new clearance once the required separation is achieved.

Quoting ThrottleHold (Reply 7):
No, they would continue on their original clearance as then everyone is aware of what each other are doing.

The should get a new clearance.

Quoting BMI727 (Reply 9):
No, this is the procedure for the NATS.

The in flight contingency procedure is essentially the same for any oceanic track, and very similar to the RVSM procedure. I doubt they were on a NAT track, I would think they would have been too far south of even track z.

Quoting Loalq (Reply 11):
No mayday call needed for this "unauthorized" emergency descend?

"Emergency" descent should be a mayday.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlinePilotaydin From Turkey, joined Sep 2004, 2539 posts, RR: 51
Reply 14, posted (4 years 11 months 1 week 5 days 18 hours ago) and read 15703 times:

Just to clear something up, this is not an emergency descent, emergency descents are associated terms with cabin pressure loss, it has nothing to do with the rate of descent etc...

The aircraft could have stayed at that altitude, but elected not to, whereas in a pressure loss, the a/c could not have stayed at that altitude...descents due to turbulence are due to passenger comfort....even if u declare an emergency and descend, it still isnt an emergecny descent...



The only time there is too much fuel onboard, is when you're on fire!
User currently offlineBorax From , joined Dec 1969, posts, RR:
Reply 15, posted (4 years 11 months 1 week 5 days 18 hours ago) and read 14830 times:

Surprised they were even on a NAT coming from ANU. Suppose it all depends on where they are placed etc...but even still. Might it have been routing above / between NAT levels?

User currently offlineAABB777 From United States of America, joined Oct 2007, 588 posts, RR: 7
Reply 16, posted (4 years 11 months 1 week 5 days 17 hours ago) and read 14268 times:
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Quoting Pilotaydin (Reply 14):
descents due to turbulence are due to passenger comfort

Not only for pax comfort but also for pax and crew safety if turbulance was as severe as reported.


User currently offlineZeke From Hong Kong, joined Dec 2006, 9210 posts, RR: 76
Reply 17, posted (4 years 11 months 1 week 5 days 16 hours ago) and read 13249 times:



Quoting Pilotaydin (Reply 14):
Just to clear something up, this is not an emergency descent, emergency descents are associated terms with cabin pressure loss, it has nothing to do with the rate of descent etc...

That is not correct, a stall for example can happen on a 777 at altitude in severe turbulence, the aircraft will depart its assigned altitude, and the cabin pressure can remain normal. This is an EMERGENCY situation.

Also in the event of an uncontrolled cabin or cargo fire, one of my first actions would be to commence an emergency descent, studies have shown that the survivability limit of the structure is between 20-30 minutes. Again cabin pressure can be normal.

Severe icing is another example where an emergency descent would be considered.

Quoting Pilotaydin (Reply 14):
The aircraft could have stayed at that altitude, but elected not to, whereas in a pressure loss, the a/c could not have stayed at that altitude...descents due to turbulence are due to passenger comfort....even if u declare an emergency and descend, it still isnt an emergecny descent...

The turbulence level reported was severe, i.e. "large, abrupt changes in altitude and/or attitude", "may be momentarily out of control". That is an EMERGENCY, not passenger comfort.

Quote:
Severe:

Aircraft Reaction: Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.

Reaction Inside Aircraft: Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food Service and walking are impossible.



Quoting Borax (Reply 15):
Surprised they were even on a NAT coming from ANU.

I have not flown that exact city pair, I would just be surprised if the track was that far north to join one of the North Atlntic Tracks (NAT).

According to the OP, it happened around N46 W30, NAT Z which is the most southern eastbound track normally routes via SOORY 42N50W 45N40W 48N30W 49N20W BEDRA NERTU. The position N46 W30 would place the aircraft 2 degrees south in latitude (i.e. 120 nm) of NAT Z crossing 30W.

http://www.turbulenceforecast.com/maps/atlantic_east.gif



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlineViscount724 From Switzerland, joined Oct 2006, 25843 posts, RR: 22
Reply 18, posted (4 years 11 months 1 week 5 days 16 hours ago) and read 13142 times:



Quoting Beansy57 (Reply 12):
ATC were unable to provide the desired descent clearance, the Captain believed his aircraft was experiencing such turbulence, he used his own authority to descend, however there are published contingency procedures on the North Atlantic Track system in place to allow you to do this, with a minimum of risk, when necessary.

It's fairly common on the North Atlantic. I included the following excerpts from the Transport Canada daily incident summaries in another recent thread. These are all from the last few months. The first one covers the BA ANU-LGW incident mentioned by the original poster in this thread.

BAW2156, British Airways Boeing 777-200, was enroute from Antigua (TAPA) to London (EGKK), at 44N040W at 05:07Z, altitude 39,000 ft. and estimating 46N030W at 05:55Z 48N020W OMOKO GUNSO. At 05:47Z, the aircraft reported severe turbulence and requested clearance for an immediate descent. At 05:49Z, Gander advised that it was unable to issue an IFR clearance due to traffic at 38,000 ft., 37,000 ft. and 36,000 ft. No rerouting was available and requested that the aircraft advise of its intentions. At 05:51Z, the aircraft reported in emergency descent from 39,000 ft to 35,000 ft. The aircraft reported traffic was visual on the Traffic Alert and Collision Avoidance System (TCAS) on route to 46N030W. At 05:54Z, the aircraft reported level at 35,000 ft.

DLH467, a Lufthansa Airbus 340-300, D-AIGO, was en route from Miami to Dusseldorf via North Atlantic Track Zulu at F380 when the flight crew requested a descent to F230 due to a cracked windshield. Gander ATC advised the crew that they were unable to issue the requested clearance due to traffic at F340 and F330. The crew of DLH467 then carried out the NAT contingency procedure turning right of track and descending to F230. Upon reaching F230, the aircraft resumed the original routing as there was no traffic at that altitude. The aircraft exited Gander oceanic airspace without further incident.

BAW5CA, British Airways Boeing 747-400, enroute from Toronto (CYYZ) to London (EGLL), routing Track "U" 49N050W at 02:35Z estimating 50N040W at 03:18Z, 35,900 ft., at 02:44Z, the aircraft reported a medical emergency, requested present position direct to Gander (CYQX). The aircraft was advised that Air Traffic Control (ATC) was unable to issue an IFR clearance due to traffic. The aircraft carried out contingency procedures and descended from 37,000 ft. to 34,000 ft. The aircraft was given clearance at 34,000 ft. direct to Gander. The flight landed at 03:49Z.

BAW66V, British Airways Boeing 777-200, enroute from Philadelphia (KPHL) to London (EGLL), declared a medical emergency and requested clearance to St. John’s (CYYT). The pilot executed contingency procedures until clear of North Atlantic (NAT) traffic and was issued clearance direct to St. John’s. The aircraft landed at 03:36Z without further incident.

ACA858, an Air Canada Airbus A-330-300, was en route from London to Toronto at F390 when the flight crew declared a PAN PAN PAN due to a passenger medical emergency. The crew requested a clearance to St. John's; however, Gander oceanic control were not able to issue the clearance due to other traffic. The crew then carried out the NAT contingency procedure and descended to F270 at which point Gander cleared the aircraft direct St. John's. The aircraft landed safely without further incident.

TSC142, an Air Transat Airbus A-310, was en route from Toronto to London at F350 when the flight crew advised Gander ACC that they were declaring a PAN situation due to a cracked windshield. The crew carried out the NAT contingency procedure and descended to F250. The crew requested a clearance to Gander and a few moments later, requested and received a clearance to St. John's. The aircraft landed safely without further incident.


User currently offlinePilotaydin From Turkey, joined Sep 2004, 2539 posts, RR: 51
Reply 19, posted (4 years 11 months 1 week 5 days 13 hours ago) and read 10467 times:



Quoting Zeke (Reply 17):

but none of those happened.....and if an a/c is stalling at a flight level in severe turbulence, the crew are at serious error there, the normal gap between low and high speed buffet even account for bank angles, a serious change in TAT would cause a stall rather than turbulence...if there is a SMALL gap between OPT and MAX altitude, then the aircraft may stall with a speed change, but for MACH to change to a stall, the TEMP would need to change drastically, otherwise a stall due to turbulence, is highly unlikely....

In my opinion, declaring an emergency is not appropriate, but that's the beauty of aviation...rules that look rigid but have loopholes...



The only time there is too much fuel onboard, is when you're on fire!
User currently offlineRobK From United Kingdom, joined Sep 2004, 3958 posts, RR: 18
Reply 20, posted (4 years 11 months 1 week 5 days 7 hours ago) and read 7803 times:



Quoting Zeke (Reply 17):
According to the OP, it happened around N46 W30, NAT Z which is the most southern eastbound track normally routes via SOORY 42N50W 45N40W 48N30W 49N20W BEDRA NERTU. The position N46 W30 would place the aircraft 2 degrees south in latitude (i.e. 120 nm) of NAT Z crossing 30W.

You're actually tieing yourself in knots here! The pic you've linked is only valid on the day you're looking at it, ie. it shows the eastbound tracks for the night of 16-17 Dec. The incident happened on 18 Oct and as the tracks change daily then the pic just confuses things because it's for a totally different day.

From my experience of listening to the NAT traffic (which is very frequent), 46n30w would be highly unlikely to be one of the tracks as it's too far south. As a general rule, the eastbound tracks are usually fairly straight across the Pond starting off the Newfoundland coast and ending off the Irish coast. The pic you've linked also confirms that to some extent too.

That said, even though the flight was probably on a random route (ie. not on the track system) there would have been all the other Caribbean-Europe traffic in the vicinity as well, either flying the same oceanic route as the BA or close by.  Smile

R


User currently offlineZeke From Hong Kong, joined Dec 2006, 9210 posts, RR: 76
Reply 21, posted (4 years 11 months 1 week 5 days 1 hour ago) and read 6458 times:



Quoting RobK (Reply 20):
The pic you've linked is only valid on the day you're looking at it,

I realize that, just like the NOPACs, no eastbound track Z today.

Quoting RobK (Reply 20):
The incident happened on 18 Oct and as the tracks change daily then the pic just confuses things because it's for a totally different day.

I didn't say the chart was the day of the incident, just explaining where the southern most track Z normally is. It states very clearly on it when it is valid.

Quoting RobK (Reply 20):
46n30w would be highly unlikely to be one of the tracks as it's too far south.

Which is exactly what I have said a few times now.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
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