B737 flight crew is informed by ATC that they are off course on the YOKES4 RNAV departing den. The F...

Attributes
ACN	1298863
Time
Date	201509
Local Time Of Day	1801-2400
Place
Locale Reference	ZDV.ARTCC
State Reference	CO
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	SID YOKES4
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 182 Flight Crew Type 6000
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 224
Events
Anomaly	Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Narrative:

We were climbing through FL310 on the YOKES4 RNAV departure; just past the yokes waypoint. ATC called and asked where we were going; he said we were off course and queried if we were on the YOKES4 departure. This caught us entirely by surprise; as we had properly verified the YOKES4 RNAV departure and all its waypoints per SOP while on the ground. ATC then queried if we had a honeywell FMS; and said that they had been having this problem with other flights. ATC said that flights had been going directly to dehli waypoint after yokes; skipping chici. This is apparently what our FMS had done as well. ATC said that this was putting aircraft into conflict with arriving aircraft to den; but that we had not been involved in a loss of separation conflict. While we had not seen it occur; apparently the chici waypoint was deleted by the FMS after it passed yokes. We reported the issue to dispatch via ACARS and the flight continued without further incident.as ATC admitted it was a known issue; a NOTAM could have prevented it. Also; ATC could have verbally warned us at any time prior to yokes so that we could be extra vigilant.

Original NASA ASRS Text

Title: B737 flight crew is informed by ATC that they are off course on the YOKES4 RNAV departing DEN. The FMC was tracking YOKES direct DEHLI and should have gone YOKES; CHICI; DEHLI. The Honeywell FMC was implicated by ATC.

Narrative: We were climbing through FL310 on the YOKES4 RNAV Departure; just past the YOKES waypoint. ATC called and asked where we were going; he said we were off course and queried if we were on the YOKES4 Departure. This caught us entirely by surprise; as we had properly verified the YOKES4 RNAV Departure and all its waypoints per SOP while on the ground. ATC then queried if we had a Honeywell FMS; and said that they had been having this problem with other flights. ATC said that flights had been going directly to DEHLI waypoint after YOKES; skipping CHICI. This is apparently what our FMS had done as well. ATC said that this was putting aircraft into conflict with arriving aircraft to DEN; but that we had not been involved in a loss of separation conflict. While we had not seen it occur; apparently the CHICI waypoint was deleted by the FMS after it passed YOKES. We reported the issue to Dispatch via ACARS and the flight continued without further incident.As ATC admitted it was a known issue; a NOTAM could have prevented it. Also; ATC could have verbally warned us at any time prior to YOKES so that we could be extra vigilant.

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.

B737 flight crew is informed by ATC that they are off course on the YOKES4 RNAV departing den. The FMC was tracking yokes direct dehli and should have gone yokes; chici; dehli. The honeywell FMC was implicated by ATC.