A crew flying non GPS B767-300 on the lfpg EVX2A RNAV was notified about a track deviation while the...

Narrative:

Our flight was cleared from lfpg as filed via EVX2A departure; runway 27L; FL100 assigned as per RNAV SID. During initial climb paris departure control assigned us a heading of 265 degrees and shortly thereafter informed us that we had deviated south of the departure course. EVX2A departure was issued to our flight on two separate occasions. The departure was loaded into the FMC and was checked against commercial chart for accuracy. Aircraft symbol was within runway parameters. All flight deck indications showed the departure to be properly flown. The captain (pilot flying) was in 5 mile scale map mode. The first officer (pilot not flying) was monitoring raw data and progress page 2. Departure was flown as per company procedures; LNAV 400 ft/left autopilot 500 ft/VNAV 1;900 ft. This aircraft is a B767-300 equipped with FMC navigation. The inherent drift in the ring laser gyro system make these aircraft unsuitable for RNAV departures. All procedures were diligently followed and all flight deck indications were well within operating parameters leading the crew to believe that the aircraft was accurately tracking the departure course. In this instance the weather was clear and visibility unrestricted. An impending conflict would have been easily detected visually. In IMC conditions; the same southerly deviation from runway 27L could be disastrous with aircraft operating from runways 26L/right.

Original NASA ASRS Text

Title: A crew flying non GPS B767-300 on the LFPG EVX2A RNAV was notified about a track deviation while the FMS indicated on track from taxi through the entire departure.

Narrative: Our flight was cleared from LFPG as filed via EVX2A Departure; Runway 27L; FL100 assigned as per RNAV SID. During initial climb Paris Departure Control assigned us a heading of 265 degrees and shortly thereafter informed us that we had deviated south of the departure course. EVX2A Departure was issued to our flight on two separate occasions. The departure was loaded into the FMC and was checked against Commercial Chart for accuracy. Aircraft symbol was within runway parameters. All flight deck indications showed the departure to be properly flown. The Captain (pilot flying) was in 5 mile scale map mode. The First Officer (pilot not flying) was monitoring raw data and progress page 2. Departure was flown as per Company procedures; LNAV 400 FT/left autopilot 500 FT/VNAV 1;900 FT. This aircraft is a B767-300 equipped with FMC navigation. The inherent drift in the ring laser gyro system make these aircraft unsuitable for RNAV departures. All procedures were diligently followed and all flight deck indications were well within operating parameters leading the crew to believe that the aircraft was accurately tracking the departure course. In this instance the weather was clear and visibility unrestricted. An impending conflict would have been easily detected visually. In IMC conditions; the same southerly deviation from Runway 27L could be disastrous with aircraft operating from Runways 26L/R.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1032858
Time
Date	201208
Local Time Of Day	1201-1800
Place
Locale Reference	LFPG.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Route In Use	SID EVX2A
Flight Plan	IFR
Component
Aircraft Component	Position Computing System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 12000
Person 2
Function	Pilot Not Flying
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

A crew flying non GPS B767-300 on the lfpg EVX2A RNAV was notified about a track deviation while the FMS indicated on track from taxi through the entire departure.