<< >> NASA ASRS Report 145327, May 1990

Flight crew of air carrier medium large transport finds that autoplt has leveled them off 300' low due to altimeter that was reading improperly.

Attributes
ACN	145327
Time
Date	199005
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dfw
State Reference	TX
Altitude	msl bound lower : 4700 msl bound upper : 5000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw tower : alb
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 171 flight time total : 8535 flight time type : 2600
ASRS Report	145327
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We were level at 5000' (as assigned by regional approach control) on radar vectors for an ILS runway 17L approach. We were IMC. The first officer was flying and the autoplt was engaged. As per company procedure the captain's and first officer's altimeters were set at QFE (29.04), with the third altimeter set at qnh (29.69). The third altimeter read 5000'. We were in level flight when the altitude alerter went off, followed by approach control telling us that altitude readout showed us at 4700', maintain 5000' altimeter 29.69. The third altimeter still showed us at 5000'. I reset my altimeter to 29.69 and it read 4800'. We climbed to 5000' on my altimeter. The third altimeter was out of tolerance. I left my altimeter set at 29.69 throughout the approach and landing. We wrote up the third altimeter and maintenance changed it. All three altimeters checked ok at the departure station. In the future I will not convert my altimeter to QFE until I am established on at least the initial approach segmet or until I am in VFR conditions, which ever comes first.

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Original NASA ASRS Text

Title: FLT CREW OF ACR MLG FINDS THAT AUTOPLT HAS LEVELED THEM OFF 300' LOW DUE TO ALTIMETER THAT WAS READING IMPROPERLY.

Narrative: WE WERE LEVEL AT 5000' (AS ASSIGNED BY REGIONAL APCH CTL) ON RADAR VECTORS FOR AN ILS RWY 17L APCH. WE WERE IMC. THE F/O WAS FLYING AND THE AUTOPLT WAS ENGAGED. AS PER COMPANY PROC THE CAPT'S AND F/O'S ALTIMETERS WERE SET AT QFE (29.04), WITH THE THIRD ALTIMETER SET AT QNH (29.69). THE THIRD ALTIMETER READ 5000'. WE WERE IN LEVEL FLT WHEN THE ALT ALERTER WENT OFF, FOLLOWED BY APCH CTL TELLING US THAT ALT READOUT SHOWED US AT 4700', MAINTAIN 5000' ALTIMETER 29.69. THE THIRD ALTIMETER STILL SHOWED US AT 5000'. I RESET MY ALTIMETER TO 29.69 AND IT READ 4800'. WE CLBED TO 5000' ON MY ALTIMETER. THE THIRD ALTIMETER WAS OUT OF TOLERANCE. I LEFT MY ALTIMETER SET AT 29.69 THROUGHOUT THE APCH AND LNDG. WE WROTE UP THE THIRD ALTIMETER AND MAINT CHANGED IT. ALL THREE ALTIMETERS CHKED OK AT THE DEP STATION. IN THE FUTURE I WILL NOT CONVERT MY ALTIMETER TO QFE UNTIL I AM ESTABLISHED ON AT LEAST THE INITIAL APCH SEGMET OR UNTIL I AM IN VFR CONDITIONS, WHICH EVER COMES FIRST.

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.