<< >> NASA ASRS Report 360518, February 1997

B767 in altitude deviation altitude excursion. Thrust management computer reduced power too much at FL390. Multiple aircraft equipment problems.

Attributes
ACN	360518
Time
Date	199702
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bdf
State Reference	IL
Altitude	msl bound lower : 38500 msl bound upper : 39000
Environment
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	360518
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
ASRS Report	360519
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other anomaly other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

ATC facility: ZAU. Location: bdf/090/50. With center autoplt in control, the aircraft was climbed from FL350 to FL390 using flight level change. Nearing FL390, altitude capture was indicated followed by altitude hold. Speed was steady at mach .80, then the tmc computer reduced thrust too much, allowing the speed to degrade to mach .75 and the aircraft began uncommanded descent. First officer applied maximum thrust and smoothly recovered to FL390. Aircraft lost approximately 500 ft. ATC said there was no conflict. Aircraft had right elevator position indicator inoperative and a history of stabilizer trim abnormalities. Also during flight we received autoplt caution messages while using right autoplt. I wrote up the stabilizer trim, right autoplt and center autoplt.

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Original NASA ASRS Text

Title: B767 IN ALTDEV ALT EXCURSION. THRUST MGMNT COMPUTER REDUCED PWR TOO MUCH AT FL390. MULTIPLE ACFT EQUIP PROBS.

Narrative: ATC FACILITY: ZAU. LOCATION: BDF/090/50. WITH CTR AUTOPLT IN CTL, THE ACFT WAS CLBED FROM FL350 TO FL390 USING FLT LEVEL CHANGE. NEARING FL390, ALT CAPTURE WAS INDICATED FOLLOWED BY ALT HOLD. SPD WAS STEADY AT MACH .80, THEN THE TMC COMPUTER REDUCED THRUST TOO MUCH, ALLOWING THE SPD TO DEGRADE TO MACH .75 AND THE ACFT BEGAN UNCOMMANDED DSCNT. FO APPLIED MAX THRUST AND SMOOTHLY RECOVERED TO FL390. ACFT LOST APPROX 500 FT. ATC SAID THERE WAS NO CONFLICT. ACFT HAD R ELEVATOR POS INDICATOR INOP AND A HISTORY OF STABILIZER TRIM ABNORMALITIES. ALSO DURING FLT WE RECEIVED AUTOPLT CAUTION MESSAGES WHILE USING R AUTOPLT. I WROTE UP THE STABILIZER TRIM, R AUTOPLT AND CTR AUTOPLT.

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.