B767 flight crew experienced a track deviation in chinese airspace approach donvo; possibly due to G...

Narrative:

We were given a 6 NM right of track offset; which we performed. The aircraft was right where it was supposed to be. We subsequently were changing our speed; when [ATC] asked if we were maintaining the offset. The captain and I were both surprised and a quick check showed that we were indeed slowly straying off the offset. I recall seeing about a 1 NM deviation at the time. The captain corrected back to the offset; and we notified ATC that we were on the offset. We were really puzzled by what happened in this event. The only two things I can think of [are]:1.the aircraft was in a turn while the FMC was still trying to compute the correction to the adjusted airspeed; therefore; the turn was not applied correctly.2. The possibility of GPS jamming. There were increased threats being made from north korea to south korea. We were aware of numerous accounts of GPS jamming according to the NOTAMS. The aircraft continued to operate well after the event. I do not believe we were more than a mile off the offset. I could be wrong; but that is what I remember seeing. [ATC] caught the deviation early; and it was a bit difficult initially to see that we were deviating since we were in a turn already. I believe we were both very alert and attentive to what the aircraft was doing; even though at the time we were engaged in changing and checking the airspeed of the aircraft via the FMC.

Original NASA ASRS Text

Title: B767 flight crew experienced a track deviation in Chinese airspace approach DONVO; possibly due to GPS jamming. ATC detects the error while it is still minor and the anomaly does not reoccur during the remainder of the flight.

Narrative: We were given a 6 NM right of track offset; which we performed. The aircraft was right where it was supposed to be. We subsequently were changing our speed; when [ATC] asked if we were maintaining the offset. The captain and I were both surprised and a quick check showed that we were indeed slowly straying off the offset. I recall seeing about a 1 NM deviation at the time. The Captain corrected back to the offset; and we notified ATC that we were on the offset. We were really puzzled by what happened in this event. The only two things I can think of [are]:1.The aircraft was in a turn while the FMC was still trying to compute the correction to the adjusted airspeed; therefore; the turn was not applied correctly.2. The possibility of GPS jamming. There were increased threats being made from North Korea to South Korea. We were aware of numerous accounts of GPS jamming according to the NOTAMS. The aircraft continued to operate well after the event. I do not believe we were more than a mile off the offset. I could be wrong; but that is what I remember seeing. [ATC] caught the deviation early; and it was a bit difficult initially to see that we were deviating since we were in a turn already. I believe we were both very alert and attentive to what the aircraft was doing; even though at the time we were engaged in changing and checking the airspeed of the aircraft via the FMC.

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.

Attributes
ACN	1289994
Time
Date	201508
Local Time Of Day	1801-2400
Place
Locale Reference	ZSHA.ARTCC
State Reference	FO
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Make Model Name	B767-300 and 300 ER
Route In Use	Other Controlled
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 133 Flight Crew Total 12700 Flight Crew Type 701
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 103 Flight Crew Total 16698 Flight Crew Type 9273
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

B767 flight crew experienced a track deviation in chinese airspace approach donvo; possibly due to GPS jamming. ATC detects the error while it is still minor and the anomaly does not reoccur during the remainder of the flight.