Flight crew of B737-300 find the LNAV mode of their FMS fails to provide proper guidance on SID out ...

Attributes
ACN	730451
Time
Date	200703
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : btg.vortac
State Reference	WA
Altitude	msl single value : 7500
Environment
Flight Conditions	IMC VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : p80.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Route In Use	departure sid : river
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 208
ASRS Report	730451
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 254 flight time type : 1800
ASRS Report	730450
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued advisory controller : issued new clearance
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

I was the pilot monitoring; the first officer was the PF. We took off runway 10R and flew river 6 departure. The first officer did a great job flying the departure on raw data (VOR/ILS). While tracking outbound on the pdx 085 degree radial; ATC gave us a vector of 030 degrees to intercept J-16. The first officer turned to the heading and I reset both VOR control heads to the battleground (btg) frequency and put the 069 degree course in both of our course windows. I crosschecked my map and verified that the LNAV data was correct and notified the first officer that LNAV was good. He then switched to LNAV while I continued to monitor the intercept off the raw data. The LNAV guidance appeared to start our turn early; I assumed the CDI (on my side) had not started to move because of how close we were to the VOR. Once the first officer had intercepted the LNAV course; it was apparent that we were right of course looking at the raw data on my side; so I directed the first officer to come back to the left and to intercept off the raw data. The first officer complied and returned to the VOR/ILS mode. The controller directed us to come back to the left and we told him we were already in the turn. The controller requested a call when we landed. When we landed we contacted the controller and he said there was a problem every day with this company flight turning early on that intercept; and said he had a training controller and forewarned her that we would be turning early. He also stated that another carrier B757 had this problem and it had something to do with their database in the aircraft. He asked me to notify a chief pilot so we could try to remedy the problem. In the future; unless I am cleared direct to a fix in the -300/-500; I will be flying only on raw data. It appears without a visual depiction of your ground track you cannot be 100% sure of an intercept close to a VOR.

Original NASA ASRS Text

Title: FLT CREW OF B737-300 FIND THE LNAV MODE OF THEIR FMS FAILS TO PROVIDE PROPER GUIDANCE ON SID OUT OF PDX. REVERT TO RAW DATA TO MONITOR RADIAL INTERCEPT.

Narrative: I WAS THE PLT MONITORING; THE FO WAS THE PF. WE TOOK OFF RWY 10R AND FLEW RIVER 6 DEP. THE FO DID A GREAT JOB FLYING THE DEP ON RAW DATA (VOR/ILS). WHILE TRACKING OUTBOUND ON THE PDX 085 DEG RADIAL; ATC GAVE US A VECTOR OF 030 DEGS TO INTERCEPT J-16. THE FO TURNED TO THE HDG AND I RESET BOTH VOR CTL HEADS TO THE BATTLEGROUND (BTG) FREQ AND PUT THE 069 DEG COURSE IN BOTH OF OUR COURSE WINDOWS. I XCHKED MY MAP AND VERIFIED THAT THE LNAV DATA WAS CORRECT AND NOTIFIED THE FO THAT LNAV WAS GOOD. HE THEN SWITCHED TO LNAV WHILE I CONTINUED TO MONITOR THE INTERCEPT OFF THE RAW DATA. THE LNAV GUIDANCE APPEARED TO START OUR TURN EARLY; I ASSUMED THE CDI (ON MY SIDE) HAD NOT STARTED TO MOVE BECAUSE OF HOW CLOSE WE WERE TO THE VOR. ONCE THE FO HAD INTERCEPTED THE LNAV COURSE; IT WAS APPARENT THAT WE WERE R OF COURSE LOOKING AT THE RAW DATA ON MY SIDE; SO I DIRECTED THE FO TO COME BACK TO THE L AND TO INTERCEPT OFF THE RAW DATA. THE FO COMPLIED AND RETURNED TO THE VOR/ILS MODE. THE CTLR DIRECTED US TO COME BACK TO THE L AND WE TOLD HIM WE WERE ALREADY IN THE TURN. THE CTLR REQUESTED A CALL WHEN WE LANDED. WHEN WE LANDED WE CONTACTED THE CTLR AND HE SAID THERE WAS A PROB EVERY DAY WITH THIS COMPANY FLT TURNING EARLY ON THAT INTERCEPT; AND SAID HE HAD A TRAINING CTLR AND FOREWARNED HER THAT WE WOULD BE TURNING EARLY. HE ALSO STATED THAT ANOTHER CARRIER B757 HAD THIS PROB AND IT HAD SOMETHING TO DO WITH THEIR DATABASE IN THE ACFT. HE ASKED ME TO NOTIFY A CHIEF PLT SO WE COULD TRY TO REMEDY THE PROB. IN THE FUTURE; UNLESS I AM CLRED DIRECT TO A FIX IN THE -300/-500; I WILL BE FLYING ONLY ON RAW DATA. IT APPEARS WITHOUT A VISUAL DEPICTION OF YOUR GND TRACK YOU CANNOT BE 100% SURE OF AN INTERCEPT CLOSE TO A VOR.

Data retrieved from NASA's ASRS site as of January 2009 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.

Flight crew of B737-300 find the LNAV mode of their FMS fails to provide proper guidance on SID out of pdx. Revert to raw data to monitor radial intercept.