B777 flight crew has altitude deviation to recover airspeed during north atlantic track entry.

Attributes
ACN	685079
Time
Date	200601
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : scrod
State Reference	FO
Altitude	msl single value : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czqx.artcc tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	685079
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	685245
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly
Independent Detector	aircraft equipment other aircraft equipment : fmc other flight crewa other flight crewb
Resolutory Action	controller : provided flight assist flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Company Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

Prior to coast out portion of flight; we received; confirmed and verified oceanic clearance to cross the north atlantic via entry point scrod FL390 mach .84 all as filed. FMC indicated maximum altitude FL396 at mach .84 (zero fuel weight update had been checked and verified during taxi to reflect concurrence with closeout numbers). Clearance was accepted and gander center cleared us direct scrod climb to and maintain FL390. After an uneventful climb and leveloff; radar service was terminated and we were switched to gander radio. As we were preparing our paperwork for the crossing and switching frequency a quick instrument scan revealed indicated airspeed decaying steadily towards minimum clean maneuver airspeed and autothrottles commanding maximum EPR. I alerted captain and began a slow descent to trade altitude for airspeed. Within 200 ft; airspeed had recovered and I leveled the aircraft at FL388. Autothrottles acted erratically and were disconnected to maintain airspeed; additionally on the FMC VNAV page maximum altitude varied between FL386 and FL396. Gander radio was informed of our inability to maintain FL390 and reclred us to maintain FL388 until able to climb. After approximately 30 mins; a slow climb (100 FPM) was initiated to maintain FL390. Throttles were operated manually until the FMC VNAV page indicated a comfortable buffer above FL390 at maximum and then re-engaged. Remainder of flight was uneventful; however; as a precaution (possible incorrect zero fuel weight at closeout) all minimum maneuver speeds were increased by 5 KTS.

Original NASA ASRS Text

Title: B777 FLT CREW HAS ALTDEV TO RECOVER AIRSPD DURING NORTH ATLANTIC TRACK ENTRY.

Narrative: PRIOR TO COAST OUT PORTION OF FLT; WE RECEIVED; CONFIRMED AND VERIFIED OCEANIC CLRNC TO CROSS THE NORTH ATLANTIC VIA ENTRY POINT SCROD FL390 MACH .84 ALL AS FILED. FMC INDICATED MAX ALT FL396 AT MACH .84 (ZERO FUEL WT UPDATE HAD BEEN CHKED AND VERIFIED DURING TAXI TO REFLECT CONCURRENCE WITH CLOSEOUT NUMBERS). CLRNC WAS ACCEPTED AND GANDER CTR CLRED US DIRECT SCROD CLB TO AND MAINTAIN FL390. AFTER AN UNEVENTFUL CLB AND LEVELOFF; RADAR SVC WAS TERMINATED AND WE WERE SWITCHED TO GANDER RADIO. AS WE WERE PREPARING OUR PAPERWORK FOR THE XING AND SWITCHING FREQ A QUICK INST SCAN REVEALED INDICATED AIRSPD DECAYING STEADILY TOWARDS MINIMUM CLEAN MANEUVER AIRSPD AND AUTOTHROTTLES COMMANDING MAX EPR. I ALERTED CAPT AND BEGAN A SLOW DSCNT TO TRADE ALT FOR AIRSPD. WITHIN 200 FT; AIRSPD HAD RECOVERED AND I LEVELED THE ACFT AT FL388. AUTOTHROTTLES ACTED ERRATICALLY AND WERE DISCONNECTED TO MAINTAIN AIRSPD; ADDITIONALLY ON THE FMC VNAV PAGE MAX ALT VARIED BTWN FL386 AND FL396. GANDER RADIO WAS INFORMED OF OUR INABILITY TO MAINTAIN FL390 AND RECLRED US TO MAINTAIN FL388 UNTIL ABLE TO CLB. AFTER APPROX 30 MINS; A SLOW CLB (100 FPM) WAS INITIATED TO MAINTAIN FL390. THROTTLES WERE OPERATED MANUALLY UNTIL THE FMC VNAV PAGE INDICATED A COMFORTABLE BUFFER ABOVE FL390 AT MAX AND THEN RE-ENGAGED. REMAINDER OF FLT WAS UNEVENTFUL; HOWEVER; AS A PRECAUTION (POSSIBLE INCORRECT ZERO FUEL WT AT CLOSEOUT) ALL MINIMUM MANEUVER SPDS WERE INCREASED BY 5 KTS.

Data retrieved from NASA's ASRS site as of January 2009 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.