Early turn on SID raises possibility of a heading track deviation with TRACON departure controller.

Attributes
ACN	187510
Time
Date	199108
Day	Thu
Local Time Of Day	1801 To 2400
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	Heavy Transport, Low Wing, 4 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude
Route In Use	departure other departure sid : sid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 9000 flight time type : 1800
ASRS Report	187510
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

In aug/91 departing seattle seatac airport on the mountain 2 departure our EFIS display DME appeared to be giving us unreliable information. According to the departure controller we turned earlier than the depicted 8 DME fix. My equipment read 8 DME initially then 9 DME then 7.8 DME, the first officer's was compatible. En route our LORAN had DME bias failure and was written up accordingly in our logbook. The departure controller did not state at what point or fix the aircraft turned on course but it's obvious we had problems then and en route with our DME and EFIS equipment. We were still able to navigate after determining whose EFIS display was inaccurate. We also told departure control of our problem.

Original NASA ASRS Text

Title: EARLY TURN ON SID RAISES POSSIBILITY OF A HDG TRACK DEV WITH TRACON DEP CTLR.

Narrative: IN AUG/91 DEPARTING SEATTLE SEATAC ARPT ON THE MOUNTAIN 2 DEP OUR EFIS DISPLAY DME APPEARED TO BE GIVING US UNRELIABLE INFO. ACCORDING TO THE DEP CTLR WE TURNED EARLIER THAN THE DEPICTED 8 DME FIX. MY EQUIP READ 8 DME INITIALLY THEN 9 DME THEN 7.8 DME, THE FO'S WAS COMPATIBLE. ENRTE OUR LORAN HAD DME BIAS FAILURE AND WAS WRITTEN UP ACCORDINGLY IN OUR LOGBOOK. THE DEP CTLR DID NOT STATE AT WHAT POINT OR FIX THE ACFT TURNED ON COURSE BUT IT'S OBVIOUS WE HAD PROBLEMS THEN AND ENRTE WITH OUR DME AND EFIS EQUIP. WE WERE STILL ABLE TO NAVIGATE AFTER DETERMINING WHOSE EFIS DISPLAY WAS INACCURATE. WE ALSO TOLD DEP CTL OF OUR PROBLEM.

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.