A B757 crew, departing lax, experienced an unwanted 5 degree left turn, when the LNAV was selected.

Attributes
ACN	538884
Time
Date	200202
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lax.airport
State Reference	CA
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Route In Use	departure sid : angel 2
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 12000 flight time type : 2000
ASRS Report	538884
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : far non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended or assigned course
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight was filed and cleared on the 'angel 2 FMS departure' from lax, daggett transition. The FMS was aligned to the airport reference point (N3356.6 W11824.5). Ground speed average after alignment was noted at 1 KT and a map comparison was made at the end of runway 25R, position was slightly north of runway depiction and not considered significant. After 400 ft AGL, LNAV was selected, the bank steering bar commanded a slight (5 degree) left turn towards the first point 'smoog' rather than commanding the 249 degree radial required. The copilot flying noticed the change and we came back right to the required heading. Airport noise procedures dictate no turns after takeoff until the smo VOR 160 degree radial. Even though we had complied with company alignment and taxi procedures the slight map deviation on departure and the proximity of the first RNAV fix resulted in a commanded turn that could conflict with required noise abatement procedures. Comments: 1) airport reference points and quick 30 second alignments do not assure accuracy during the initial phase of RNAV departures. 2) 10 NM scale map displays are not accurate enough to access map/FMS deviation. 3) there are no engine or runway coordinates available except by the latitude/longitude scale on the airport page, easy to make mistakes. 4) there are no raw data references on RNAV departures and airways to check for map drift, or back-up in case of map failure.

Original NASA ASRS Text

Title: A B757 CREW, DEPARTING LAX, EXPERIENCED AN UNWANTED 5 DEG L TURN, WHEN THE LNAV WAS SELECTED.

Narrative: FLT WAS FILED AND CLRED ON THE 'ANGEL 2 FMS DEP' FROM LAX, DAGGETT TRANSITION. THE FMS WAS ALIGNED TO THE ARPT REF POINT (N3356.6 W11824.5). GND SPD AVERAGE AFTER ALIGNMENT WAS NOTED AT 1 KT AND A MAP COMPARISON WAS MADE AT THE END OF RWY 25R, POS WAS SLIGHTLY N OF RWY DEPICTION AND NOT CONSIDERED SIGNIFICANT. AFTER 400 FT AGL, LNAV WAS SELECTED, THE BANK STEERING BAR COMMANDED A SLIGHT (5 DEG) L TURN TOWARDS THE FIRST POINT 'SMOOG' RATHER THAN COMMANDING THE 249 DEG RADIAL REQUIRED. THE COPLT FLYING NOTICED THE CHANGE AND WE CAME BACK RIGHT TO THE REQUIRED HDG. ARPT NOISE PROCS DICTATE NO TURNS AFTER TKOF UNTIL THE SMO VOR 160 DEG RADIAL. EVEN THOUGH WE HAD COMPLIED WITH COMPANY ALIGNMENT AND TAXI PROCS THE SLIGHT MAP DEV ON DEP AND THE PROX OF THE FIRST RNAV FIX RESULTED IN A COMMANDED TURN THAT COULD CONFLICT WITH REQUIRED NOISE ABATEMENT PROCS. COMMENTS: 1) ARPT REF POINTS AND QUICK 30 SECOND ALIGNMENTS DO NOT ASSURE ACCURACY DURING THE INITIAL PHASE OF RNAV DEPS. 2) 10 NM SCALE MAP DISPLAYS ARE NOT ACCURATE ENOUGH TO ACCESS MAP/FMS DEV. 3) THERE ARE NO ENG OR RWY COORDINATES AVAILABLE EXCEPT BY THE LATITUDE/LONGITUDE SCALE ON THE ARPT PAGE, EASY TO MAKE MISTAKES. 4) THERE ARE NO RAW DATA REFS ON RNAV DEPS AND AIRWAYS TO CHK FOR MAP DRIFT, OR BACK-UP IN CASE OF MAP FAILURE.

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.