<< >> NASA ASRS Report 639472, December 2004

MD80 pms failure to maintain planned cruise speed allows mach to fall to pt 67 from pt 76 when at FL370 10 NM south of sav.

Attributes
ACN	639472
Time
Date	200412
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : sav.vortac
State Reference	GA
Altitude	msl single value : 37000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	639472
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence other other anomaly
Independent Detector	aircraft equipment other aircraft equipment : air speed ind/ mach other flight crewa other flight crewb
Resolutory Action	aircraft : equipment problem dissipated flight crew : overcame equipment problem flight crew : overrode automation other
Consequence	other other Other
Supplementary
Problem Areas	Maintenance Human Performance Flight Crew Human Performance Company Aircraft
Primary Problem	Aircraft

Narrative:

Pms failure in cruise resulting in large loss of airspeed. We were using pms in the optimum cruise mode at FL370, which resulted in a cruise mach of approximately .76. After 1 1/2 hours, the pms quickly and smoothly began reducing speed. We caught it at .67 (approximately 220 KIAS). The pms then defaulted back to .79 mach as an optimum. Status check indicated no faults. After another +/-30 mins, it settled back down to .76 optimum. All predep into was correctly entered and the pms was operated correctly. We were making no entries when the event occurred. There was no altitude deviation. Based on recent events regarding high altitude stalls, this could be a contributing factor. The pms was written up in the log upon arrival at lga.

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Original NASA ASRS Text

Title: MD80 PMS FAILURE TO MAINTAIN PLANNED CRUISE SPD ALLOWS MACH TO FALL TO PT 67 FROM PT 76 WHEN AT FL370 10 NM S OF SAV.

Narrative: PMS FAILURE IN CRUISE RESULTING IN LARGE LOSS OF AIRSPD. WE WERE USING PMS IN THE OPTIMUM CRUISE MODE AT FL370, WHICH RESULTED IN A CRUISE MACH OF APPROX .76. AFTER 1 1/2 HRS, THE PMS QUICKLY AND SMOOTHLY BEGAN REDUCING SPD. WE CAUGHT IT AT .67 (APPROX 220 KIAS). THE PMS THEN DEFAULTED BACK TO .79 MACH AS AN OPTIMUM. STATUS CHK INDICATED NO FAULTS. AFTER ANOTHER +/-30 MINS, IT SETTLED BACK DOWN TO .76 OPTIMUM. ALL PREDEP INTO WAS CORRECTLY ENTERED AND THE PMS WAS OPERATED CORRECTLY. WE WERE MAKING NO ENTRIES WHEN THE EVENT OCCURRED. THERE WAS NO ALTDEV. BASED ON RECENT EVENTS REGARDING HIGH ALT STALLS, THIS COULD BE A CONTRIBUTING FACTOR. THE PMS WAS WRITTEN UP IN THE LOG UPON ARR AT LGA.

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.