A300
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Aircraft; Environment - Non Weather Related
Prior to descent into ELP; we started to lose GPS signals. The 'GPS not Primary' caution came and went out a number of times until we lost all GPS signals. We were cleared to descend via the SAMMR 2 RNAV arrival. Albuquerque Center asked us if we would be able to make the arrival; which resulted in a discussion between the First Officer and I about our ability to make the airspeed and altitude restrictions as depicted on the arrival. We agreed that we were able to make all restrictions and relayed that to ABQ Center who then deleted the arrival restrictions. At this point I was really confused as to what they were seeing that we were not. We continued the arrival and met all restrictions anyway; followed by radar vectors to a visual 22 backed up by the ILS. During the approach phase we received the 'NAV accuracy downgrade' caution that you would expect with a loss of GPS. After landing; we talked to Ground/Tower who informed us that other aircraft had experienced loss of GPS. Then; two other company flights that were on that frequency said that they had also lost all GPS reception. There was no NOTAM information indicating a possible GPS disruption. I talked to Dispatch the next morning and they were unaware that there was a problem with GPS reception in the ELP area; but on further research; they did find an obscure reference to the outage on the FAA's website. Later; I did manage to find an ABQ ARTCC NOTAM on the iPad; iPhone app 'HD NOTAMs' that did discuss the possibility of GPS loss in the ELP area. NOTAM follows; NAV GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A RADIUS OF 479 NM CENTERED AT 323259N/1060123W OR THE LOCATION ALSO KNOWN AS THE EL PASO VOR /ELP/ 017 DEGREE RADIAL AT 46 NM AT FL400 AND ABOVE; DECREASING IN AREA WITH A DECREASE IN ALTITUDE TO A RADIUS OF 424 NM AT FL250; A RADIUS 337 NM AT 10;000 FT MSL; A RADIUS OF 354 NM AT 4;000 FT AGL AND A RADIUS OF 264 NM AT 50 FT AGL. This NOTAM had been running for several days. The unexpected loss of GPS signal raises several areas of concern. 1. Unexpected loss of GPS in flight is such a rare occurrence that it creates a distraction in the cockpit. 2. Loosing GPS may affect the legality of flying an RNAV arrival; and the whole process of checking for required RNP is not something that immediately; in flight; comes to mind. Whereas; knowing of a possible outage in advance would allow the crew time to check on equipment requirements for a particular arrival. 3. Loss of GPS signal can affect the legality of flying RNAV approaches; and it would be helpful to have time (preflight) to consider this. 4. Loss of GPS coverage can affect the legality and practicality of filing RNAV only airways. Although the Airbus triple mix IRU's with DME updating mitigates some of the above items; the time to discuss this ideally takes place in the preflight phase; rather than in the arrival and approach phase. 5. Don't leave any nagging doubts about what you are seeing or hearing. Even though the restrictions had been lifted for us on the SAMMR 2 arrival; I still had plenty of doubts about what ABQ knew that we didn't; the discussion never went any farther than a lifting of the restrictions on the arrival. I should have asked specifically what their concern was rather than assuming that it was about our ability to meet restrictions. In hindsight I think they were concerned about the possible loss of RNAV capability because of the GPS outage. It sure used up a lot of brain power second guessing what I was seeing on the FMS display (ND). 6. As you can see the above FAA NOTAM is unnecessarily verbose and consideration should be given to putting it out in an abbreviated format along with the NOTAMs normally included in our flight paperwork. Something that is airport specific; (for arrivals and approaches) and that covers en route portions of flight that passes through the affected area. Lastly and most importantly; as soon as a loss of GPS in detected; it should immediately be reported to the controlling agency; even if it doesn't affect your required RNP. Had I done this; it might have cleared up all of the confusion from the get go. The event was caused by whatever agency was fiddling with the GPS signal. NOTAM about GPS outage included in normal flight paperwork.
A300 Captain describes a loss of GPS during arrival to ELP. After the fact a NOTAM is discovered describing the outage.