Air carrier widebody transport on oceanic north atlantic track encounters severe clear air turbulence and captain cites use of command decision to alter course in a heading track altitude deviation when high frequency communication is unavailable garbled congested on frequency.

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Attributes
ACN	167793
Time
Date	199101
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zny
State Reference	NY
Altitude	msl bound lower : 31000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny tower : mci
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : other oceanic enroute : atlantic enroute airway : zny
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 8600
ASRS Report	167793
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 25000 flight time type : 600
ASRS Report	167574
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter other non adherence : clearance non adherence : far other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : exited adverse environment other
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation other
Situations
ATC Facility	other physical facility procedure or policy : unspecified

Narrative:

While flying at FL370 on 1/thur/91, widebody transport airlines flight on north atlantic track G started to encounter moderate turbulence as we approached 43 degrees north, 60 degrees west. At this point we contacted ny radio on high frequency and requested lower. Was told to stand by. Turbulence proceeded to get worse and additional requests for lower were made, with the last request for an immediate descent. Now in severe turbulence and ny unable to give us a clearance, the captain elected to turn off track and initiate a descent. At this point, approximately 43 degrees north, 65 degrees west, I was able VHF contact with ZBW and told them we were off track and leveling at FL310. Shortly thereafter, ZBW issued a clearance direct alk at FL310. With VFR conditions and excellent visibility, no other traffic was observed. Supplemental information from acn 167574: told to stand by 4 times. High frequency was garbled and hard to contact ny oceanic. Captain considered the loss of the aircraft due to unusual attitudes and structural failure. The first officer told ny oceanic that aircraft was turning 45 degrees port (off track) and descending to 31000'. Approximately 33000', smooth air encountered and ZBW was contacted. Using command decision the captain had turned off track and descended west/O clearance.

Original NASA ASRS Text

Title: ACR WDB ON OCEANIC NORTH ATLANTIC TRACK ENCOUNTERS SEVERE CLEAR AIR TURBULENCE AND CAPT CITES USE OF COMMAND DECISION TO ALTER COURSE IN A HEADING TRACK ALT DEVIATION WHEN HIGH FREQ COM IS UNAVAILABLE GARBLED CONGESTED ON FREQ.

Narrative: WHILE FLYING AT FL370 ON 1/THUR/91, WDB AIRLINES FLT ON N ATLANTIC TRACK G STARTED TO ENCOUNTER MODERATE TURB AS WE APCHED 43 DEGS N, 60 DEGS W. AT THIS POINT WE CONTACTED NY RADIO ON HIGH FREQ AND REQUESTED LOWER. WAS TOLD TO STAND BY. TURB PROCEEDED TO GET WORSE AND ADDITIONAL REQUESTS FOR LOWER WERE MADE, WITH THE LAST REQUEST FOR AN IMMEDIATE DSNT. NOW IN SEVERE TURB AND NY UNABLE TO GIVE US A CLRNC, THE CAPT ELECTED TO TURN OFF TRACK AND INITIATE A DSNT. AT THIS POINT, APPROX 43 DEGS N, 65 DEGS W, I WAS ABLE VHF CONTACT WITH ZBW AND TOLD THEM WE WERE OFF TRACK AND LEVELING AT FL310. SHORTLY THEREAFTER, ZBW ISSUED A CLRNC DIRECT ALK AT FL310. WITH VFR CONDITIONS AND EXCELLENT VISIBILITY, NO OTHER TFC WAS OBSERVED. SUPPLEMENTAL INFO FROM ACN 167574: TOLD TO STAND BY 4 TIMES. HIGH FREQ WAS GARBLED AND HARD TO CONTACT NY OCEANIC. CAPT CONSIDERED THE LOSS OF THE ACFT DUE TO UNUSUAL ATTITUDES AND STRUCTURAL FAILURE. THE F/O TOLD NY OCEANIC THAT ACFT WAS TURNING 45 DEGS PORT (OFF TRACK) AND DSNDING TO 31000'. APPROX 33000', SMOOTH AIR ENCOUNTERED AND ZBW WAS CONTACTED. USING COMMAND DECISION THE CAPT HAD TURNED OFF TRACK AND DSNDED W/O CLRNC.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.