An aircraft flight crew attempted to enter a 1R in between fixes on a north atlantic track. The FMS ...

Attributes
ACN	1240732
Time
Date	201502
Place
Locale Reference	EGGX.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Widebody Low Wing 3 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Oceanic
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Experience	Flight Crew Last 90 Days 118 Flight Crew Total 9000 Flight Crew Type 3032
Person 2
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 10469 Flight Crew Type 2561
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Less Severe Deviation - Procedural FAR Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

Our aircraft had just made the turn passing 58n020w towards 59n030w. The FMS had cycled through these points correctly. I elected to enter a slop of 1 nm right; by using the normal procedure of a lateral offset off ll; and inputting a 1 mile right offset into the offset prompt. I then selected the prompt to input the offset. The FMS flight plan then changed with a t-p as the from point (instead of 58n020w) and showed 59n040w as next (instead of 59n030w). We immediately noticed this discrepancy. We called up the secondary flight plan; confirmed the correct waypoint sequence; and activated the secondary flight plan; and the aircraft remained on track to 59n030w. We received an automated ads shortly thereafter stating 'ads position reporting indicates that you are deviating from cleared route / indications are that you are routing direct to your 40W coordinate / please check and confirm your next waypoint'. We immediately resent the position report showing the correct waypoint sequence. At no time was the aircraft off course. I do not have an explanation for why the FMS behaved as it did. Vigilent adherence to waypoint passage procedures; kept this event from becoming a gross nav error.

Original NASA ASRS Text

Title: An aircraft flight crew attempted to enter a 1R in between fixes on a North Atlantic Track. The FMS dropped the proper 'from' waypoint and also dropped the proper 'to' waypoint. They activated the secondary flight plan and remained on course.

Narrative: Our aircraft had just made the turn passing 58N020W towards 59N030W. The FMS had cycled through these points correctly. I elected to enter a SLOP of 1 nm right; by using the normal procedure of a lateral offset off lL; and inputting a 1 mile right offset into the offset prompt. I then selected the prompt to input the offset. The FMS flight plan then changed with a T-P as the from point (instead of 58N020W) and showed 59N040W as next (instead of 59N030W). We immediately noticed this discrepancy. We called up the secondary flight plan; confirmed the correct waypoint sequence; and activated the secondary flight plan; and the aircraft remained on track to 59N030W. We received an automated ADS shortly thereafter stating 'ADS position reporting indicates that you are deviating from cleared route / indications are that you are routing direct to your 40W coordinate / please check and confirm your next waypoint'. We immediately resent the position report showing the correct waypoint sequence. At no time was the aircraft off course. I do not have an explanation for why the FMS behaved as it did. Vigilent adherence to waypoint passage procedures; kept this event from becoming a gross nav error.

Data retrieved from NASA's ASRS site 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.

An aircraft flight crew attempted to enter a 1R in between fixes on a north atlantic track. The FMS dropped the proper 'from' waypoint and also dropped the proper 'to' waypoint. They activated the secondary flight plan and remained on course.