Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
General None Reported / Taken
Aircraft
I recently submitted a [safety report] to report problems with MD-80 FMS operations on some of the new RNAV arrivals into DFW. Yesterday; I received a close out message that stated that the MD-80 Fleet Captain had been notified and was aware of issue. Today I had an almost exact repeat of the issue in a different FMS-equipped aircraft on the BOOVE 1 RNAV arrival.During operation to DFW; I encountered a problem with the FMS operation. Shortly after departure; I noticed that the FMS was not computing ETA's and predicted fuel for the next waypoint and destination. I confirmed that all the necessary information was entered correctly into the FMS. Having seen this problem before and realizing that the VNAV function of the FMS would likely not be available; I thoroughly briefed the FO on alternate procedures we would use to comply with the numerous restrictions on the BOOVE Arrival. As we approached the beginning of the arrival; all VNAV information to include TOD point; the Vertical Deviation Indication (VDI) and scale were not present and remained unavailable during the arrival. We executed the descent using the airspeed and vertical speed modes of the autopilot. The 'green arc' altitude crossing indicator did function normally and provided altitude prediction guidance as we stepped through each of the altitude constraints. All lateral; speed; and vertical constraints were complied with. After passing the last waypoint on the arrival and while transitioning to the instrument approach; the VNAV and associated VDI displayed functions returned and appeared to operate normally. The close out message on my previous report suggests that this is a KNOWN ANOMALY with MD-80 FMS aircraft. While some knowledge of this problem is anecdotally passed around among MD-80 crews; I do not recall seeing any official guidance from our fleet managers regarding this issue and suggested alternate procedures to manage these high-workload RNAV arrivals.We recently received a company message regarding the importance of making smooth; constant rate descents on the new RNAV arrivals into DFW. The absence of a functioning VNAV makes this goal all the more difficult. I highly suggest that the MD-80 fleet team put together some type of communication regarding the limitations and possible degraded operating modes of the FMS system when dealing with complex RNAV arrivals to include guidance on how to best comply with the stringent altitude and speed constraints in the absence of any VNAV guidance. I would also suggest that it be made a HOT ITEM by the training department and include a related training module in our next training cycle.
MD-80 Captain described limitations of his aircraft FMS that makes flying complex DFW RNAV arrivals difficult.