Track deviation caused by a ground power failure.

Attributes
ACN	315800
Time
Date	199509
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sea
State Reference	WA
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sea
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	climbout : initial
Route In Use	departure : noise abatement departure other departure sid : sid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 14000 flight time type : 7000
ASRS Report	315800
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 110 flight time total : 15000 flight time type : 9500
ASRS Report	315888
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : published procedure non adherence other other anomaly other other spatial deviation
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Air Traffic Incident	Pilot Deviation

Narrative:

While departing runway 34R at seattle on the summa 5 departure, I made a slight left turn to intercept the 338 degree radial of sea. Apparently my HSI card drifted approximately 20 degrees to the right. The HSI needle then indicated left of course. A correction was made to the right to a heading of 360 degrees to get back on the 338 degree radial. I did not realize that the compass information on my HSI was in error. The compass switch was in the slaved position and the compass system worked normally on the previous leg. Departure control advised us at approximately 7 DME that we were about 1 mi left of course and told us to come right to intercept the 338 degree radial 'for noise abatement.' the captain realized that my heading information was in error and so advised me. I went to directional gyroscope mode and slewed the compass to agree with the captain's. The remainder of the SID was flown as published. Once at cruise, the compass was again tried in the slaved mode and it worked normally for the remainder of the flight. While on the ground in seattle, approximately 25 mins prior to takeoff, the ground power failed and the aircraft was without power for approximately 5 mins.

Original NASA ASRS Text

Title: TRACK DEV CAUSED BY A GND PWR FAILURE.

Narrative: WHILE DEPARTING RWY 34R AT SEATTLE ON THE SUMMA 5 DEP, I MADE A SLIGHT L TURN TO INTERCEPT THE 338 DEG RADIAL OF SEA. APPARENTLY MY HSI CARD DRIFTED APPROX 20 DEGS TO THE R. THE HSI NEEDLE THEN INDICATED L OF COURSE. A CORRECTION WAS MADE TO THE R TO A HDG OF 360 DEGS TO GET BACK ON THE 338 DEG RADIAL. I DID NOT REALIZE THAT THE COMPASS INFO ON MY HSI WAS IN ERROR. THE COMPASS SWITCH WAS IN THE SLAVED POS AND THE COMPASS SYS WORKED NORMALLY ON THE PREVIOUS LEG. DEP CTL ADVISED US AT APPROX 7 DME THAT WE WERE ABOUT 1 MI L OF COURSE AND TOLD US TO COME R TO INTERCEPT THE 338 DEG RADIAL 'FOR NOISE ABATEMENT.' THE CAPT REALIZED THAT MY HDG INFO WAS IN ERROR AND SO ADVISED ME. I WENT TO DIRECTIONAL GYROSCOPE MODE AND SLEWED THE COMPASS TO AGREE WITH THE CAPT'S. THE REMAINDER OF THE SID WAS FLOWN AS PUBLISHED. ONCE AT CRUISE, THE COMPASS WAS AGAIN TRIED IN THE SLAVED MODE AND IT WORKED NORMALLY FOR THE REMAINDER OF THE FLT. WHILE ON THE GND IN SEATTLE, APPROX 25 MINS PRIOR TO TKOF, THE GND PWR FAILED AND THE ACFT WAS WITHOUT PWR FOR APPROX 5 MINS.

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.