B737-300 flight crew departing runway 18L at clt via the meril 6 RNAV experiences a track deviation ...

Narrative:

Runway 18L meril 6 RNAV departure to hisor; first officer was flying. Departure was briefed at gate; we both verified heading; altitude; departure procedure. VNAV was called for and engaged at 400 ft. Autopilot was engaged at 1;000 ft. First officer called for flaps 1. Just as I selected flaps 1 I noticed the control wheel roll to the right. I was surprised as it is basically a straight out departure. As I looked at the compass; the autopilot press to reset light started flashing in front of me and I noticed that our heading was about 200-205. The first officer had overridden the autopilot and was initiating a turn back to the departure course. At the same time the controller was telling us to turn left 20 degrees; that we had traffic to our right departing off of 18C. We both saw the other aircraft slightly ahead at about our altitude. We never got a warning from the TCAS. We then recoupled the autopilot and resumed the departure with no further problems. I have no idea as to why this happened. Everything was set up correctly and we followed all of the RNAV departure procedures. As I first noticed the wheel rolling to the right I thought that it might be correcting for the strong westerly winds that were programmed into the FMC for the flight; but it way over-corrected if that was the case. As I don't know why this happened I can't really suggest anything. The first officer did an excellent job of catching the problem as quickly as he did and over-riding the autopilot.

Original NASA ASRS Text

Title: B737-300 flight crew departing Runway 18L at CLT via the MERIL 6 RNAV experiences a track deviation when the autopilot is engaged at 1;000 FT AGL. The flying First Officer aggressively returns the aircraft to the desired track as ATC is noting the deviation.

Narrative: Runway 18L Meril 6 RNAV departure to HISOR; First Officer was flying. Departure was briefed at gate; we both verified heading; altitude; departure procedure. VNAV was called for and engaged at 400 FT. Autopilot was engaged at 1;000 FT. First Officer called for flaps 1. Just as I selected flaps 1 I noticed the control wheel roll to the right. I was surprised as it is basically a straight out departure. As I looked at the compass; the Autopilot press to reset light started flashing in front of me and I noticed that our heading was about 200-205. The First Officer had overridden the autopilot and was initiating a turn back to the departure course. At the same time the Controller was telling us to turn left 20 degrees; that we had traffic to our right departing off of 18C. We both saw the other aircraft slightly ahead at about our altitude. We never got a warning from the TCAS. We then recoupled the autopilot and resumed the departure with no further problems. I have no idea as to why this happened. Everything was set up correctly and we followed all of the RNAV departure procedures. As I first noticed the wheel rolling to the right I thought that it might be correcting for the strong westerly winds that were programmed into the FMC for the flight; but it way over-corrected if that was the case. As I don't know why this happened I can't really suggest anything. The First Officer did an excellent job of catching the problem as quickly as he did and over-riding the autopilot.

Data retrieved from NASA's ASRS site as of April 2012 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	986076
Time
Date	201112
Local Time Of Day	1201-1800
Place
Locale Reference	CLT.Airport
State Reference	NC
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

B737-300 flight crew departing runway 18L at clt via the meril 6 RNAV experiences a track deviation when the autopilot is engaged at 1;000 ft AGL. The flying first officer aggressively returns the aircraft to the desired track as ATC is noting the deviation.