B732 crew didn't notice malfunctioning compass system until shortly after takeoff.

Attributes
ACN	496630
Time
Date	200101
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lga.airport
State Reference	NY
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : vacating altitude climbout : takeoff
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 600
ASRS Report	496630
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe other anomaly other other spatial deviation
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : landed as precaution
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

We departed lga runway 31 with heading errors on both compass system of approximately 30-35 degrees. It was the same error on both system as verified by the standby compass. Working with ATC, we attempted to navigation directly to a NAVAID. Unable to do so with precision. Flight diverted to bwi for an uneventful landing. Things that contributed to this: 1) short taxi from gate to end of runway. Less time to catch an error. 2) same exact error on 2 independent system. 3) heading bug set to assigned turn on SID which happened to be the runway heading, therefore on takeoff, bug was in position it normally is in for a 'takeoff to runway heading.'

Original NASA ASRS Text

Title: B732 CREW DIDN'T NOTICE MALFUNCTIONING COMPASS SYS UNTIL SHORTLY AFTER TKOF.

Narrative: WE DEPARTED LGA RWY 31 WITH HDG ERRORS ON BOTH COMPASS SYS OF APPROX 30-35 DEGS. IT WAS THE SAME ERROR ON BOTH SYS AS VERIFIED BY THE STANDBY COMPASS. WORKING WITH ATC, WE ATTEMPTED TO NAV DIRECTLY TO A NAVAID. UNABLE TO DO SO WITH PRECISION. FLT DIVERTED TO BWI FOR AN UNEVENTFUL LNDG. THINGS THAT CONTRIBUTED TO THIS: 1) SHORT TAXI FROM GATE TO END OF RWY. LESS TIME TO CATCH AN ERROR. 2) SAME EXACT ERROR ON 2 INDEPENDENT SYS. 3) HDG BUG SET TO ASSIGNED TURN ON SID WHICH HAPPENED TO BE THE RWY HDG, THEREFORE ON TKOF, BUG WAS IN POS IT NORMALLY IS IN FOR A 'TKOF TO RWY HDG.'

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.