Unable to maintain altitude account mountain wave and gross weight of aircraft.

Attributes
ACN	81279
Time
Date	198801
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : hlc
State Reference	KS
Altitude	msl bound lower : 38600 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute airway : j64
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 200
ASRS Report	81279
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : flight engineer pilot : instrument pilot : atp
Experience	flight time last 90 days : 150 flight time total : 8000 flight time type : 200
ASRS Report	81176
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : weather non adherence : required legal separation other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were clrd from FL350 to FL390. Over hill city VOR at approximately 370, center asked if we could be level FL390 in 4 mins. We said yes. I adjusted climb rate on autoplt to approximately 600 FPM. As we climbed, our speed deteriorated from .82 mach to .77. As we leveled off, speed fell further to .725 (225 KTS). We also seemed to encounter a mtn wave. We had selected mct on the autothrottles, but we could barely maintain speed. I punched off autothrottles and autoplt, but could not maintain speed and altitude. We encountered light to moderate chop and altitude decreased to FL386 before we could get clearance to FL370. There was traffic right below us at FL370. We finally turned and descended which solved the problem. We did, however, encounter low speed buffet and came very close to stalling at FL390, which would have been unhealthy, to say the least. This aircraft has the characteristic of sort of dying in the last few thousand feet of climb. I knew this, and should have told center that I could not maintain climb rate. This put us very close to the back side of the power curve. The mtn wave did the rest. Next time I won't be so helpful and take a vector for climb as necessary. According to the book, we were legal for the altitude. At our weight, we needed .82-.83 mach, however. Supplemental information from acn 81176: as we leveled off at FL390 we hit a mtn wave activity and turbulence with the speed falling off to .725 mach (225 KTS). At this point we selected maximum count power (mct). The speed still was deteriorating and to try to maintain speed because we were so close to a stall our altitude went down to 38600' and encountered a low speed buffet. Supplemental information from acn 81377: we requested lower altitude and aircraft seemed to be getting closer to a low speed buffet. Center turned us 40 degrees and approved FL370. Altitude had decreased during all this to FL386 before center had clrd us down to FL370.

Original NASA ASRS Text

Title: UNABLE TO MAINTAIN ALT ACCOUNT MOUNTAIN WAVE AND GROSS WEIGHT OF ACFT.

Narrative: WE WERE CLRD FROM FL350 TO FL390. OVER HILL CITY VOR AT APPROX 370, CENTER ASKED IF WE COULD BE LEVEL FL390 IN 4 MINS. WE SAID YES. I ADJUSTED CLB RATE ON AUTOPLT TO APPROX 600 FPM. AS WE CLBED, OUR SPD DETERIORATED FROM .82 MACH TO .77. AS WE LEVELED OFF, SPD FELL FURTHER TO .725 (225 KTS). WE ALSO SEEMED TO ENCOUNTER A MTN WAVE. WE HAD SELECTED MCT ON THE AUTOTHROTTLES, BUT WE COULD BARELY MAINTAIN SPD. I PUNCHED OFF AUTOTHROTTLES AND AUTOPLT, BUT COULD NOT MAINTAIN SPD AND ALT. WE ENCOUNTERED LIGHT TO MODERATE CHOP AND ALT DECREASED TO FL386 BEFORE WE COULD GET CLRNC TO FL370. THERE WAS TFC RIGHT BELOW US AT FL370. WE FINALLY TURNED AND DESCENDED WHICH SOLVED THE PROB. WE DID, HOWEVER, ENCOUNTER LOW SPD BUFFET AND CAME VERY CLOSE TO STALLING AT FL390, WHICH WOULD HAVE BEEN UNHEALTHY, TO SAY THE LEAST. THIS ACFT HAS THE CHARACTERISTIC OF SORT OF DYING IN THE LAST FEW THOUSAND FEET OF CLB. I KNEW THIS, AND SHOULD HAVE TOLD CENTER THAT I COULD NOT MAINTAIN CLB RATE. THIS PUT US VERY CLOSE TO THE BACK SIDE OF THE PWR CURVE. THE MTN WAVE DID THE REST. NEXT TIME I WON'T BE SO HELPFUL AND TAKE A VECTOR FOR CLB AS NECESSARY. ACCORDING TO THE BOOK, WE WERE LEGAL FOR THE ALT. AT OUR WT, WE NEEDED .82-.83 MACH, HOWEVER. SUPPLEMENTAL INFORMATION FROM ACN 81176: AS WE LEVELED OFF AT FL390 WE HIT A MTN WAVE ACTIVITY AND TURBULENCE WITH THE SPD FALLING OFF TO .725 MACH (225 KTS). AT THIS POINT WE SELECTED MAX COUNT PWR (MCT). THE SPD STILL WAS DETERIORATING AND TO TRY TO MAINTAIN SPD BECAUSE WE WERE SO CLOSE TO A STALL OUR ALT WENT DOWN TO 38600' AND ENCOUNTERED A LOW SPD BUFFET. SUPPLEMENTAL INFORMATION FROM ACN 81377: WE REQUESTED LOWER ALT AND ACFT SEEMED TO BE GETTING CLOSER TO A LOW SPD BUFFET. CENTER TURNED US 40 DEGS AND APPROVED FL370. ALT HAD DECREASED DURING ALL THIS TO FL386 BEFORE CENTER HAD CLRD US DOWN TO FL370.

Data retrieved from NASA's ASRS site as of August 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.