Gulfstream G200 (IAI 1126 Galaxy)
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 69; Flight Crew Total 4364; Flight Crew Type 2085
Distraction; Time Pressure
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
ATC Equipment / Nav Facility / Buildings; Aircraft; Human Factors
In oceanic cruise westbound between Greenland and Canada; the aircraft experienced a simultaneous loss of GPS position information on both GPS sensors. Both primary flight displays annunciated the 'POS' (position uncertain) indication; and a check of the message page on the FMS confirmed that both GPS sensors had dropped back to acquire mode with no GPS position displayed. An immediate reversion to FMS dead reckoning created some confusion in the cockpit; as both pilots expected a reversion to IRS navigation with minimal degradation of position uncertainty. This did not occur; however. FMS navigation remained in dead reckoning; and positional uncertainty started to increase. The pilots discussed the feasibility of tracking the outbound course from the OZN radio beacon on Greenland as a temporary measure to remain on our cleared track towards the coast-in fix. The distance from the beacon was too far: the display of the ADF needle was too erratic; and the audio identifier had become too faint. Then; the GPS position was reacquired by both sensors; albeit temporarily; and the FMS continued to navigate. The GPS sensors subsequently lost position a second and third time; having re-established position for perhaps 2 or 3 minutes each time they recovered. After the third occurrence; the airplane was inside of 30 minutes to the coast-in fix. At this point a decision to dead reckon using the magnetic heading on the computer-generated navigation log was agreed upon by both pilots as the best course of action to keep the airplane as close as possible to its assigned track; given the circumstances. A call to domestic ATC was made 5 minutes prior to coast-in fix. Radar contact was established; and the Controller advised we should update our position; as it appeared we would pass nearly 20 miles south of the fix. We were subsequently cleared to a VOR that we were by then receiving; the remainder of the flight was uneventful.Reviewing the events; I identified two areas where the level of crew coordination was not where it needed to be in all phases of this flight. First; as pilot not flying; I allowed myself to become preoccupied with the loss of GPS sensor data; and this had a negative impact on communications. Although the pilot flying and I were communicating effectively as to what problems we were facing; I should have advised ATC much sooner of the situation and what our intentions would be; rather than try and get everything figured out first. Second; the source of our IRS failure to navigate: human error. Upon landing; I observed the mode knob had not been fully turned to the alignment detent during preflight in Europe. Consequently; what we saw on the IRS was a blank panel (off); which also happens to be exactly what the pilot sees when the system is in normal operating mode. This type of error cannot be corrected in flight. From a crew coordination standpoint; factors external to cockpit duties such as passenger and baggage loading; fueling; etc can effectively take one pilot out of the equation during the preflight setup of the cockpit; and this situation is best remedied by having procedures and habit patterns in place to ensure both pilots are double checking vital systems such as an FMS or; in this case; an IRS are properly configured; especially prior to extended over water flights. On this particular flight; last-minute servicing items and a looming departure slot time caused a breakdown in these habit patterns; and something as basic as the position of a knob was overlooked.
G200 Captain experiences loss of GPS navigation capability on the North Atlantic Tracks westbound with the FMS reverting to dead reckoning and not IRS navigation as expected. ATC indicates the flight is 20 NM south of course upon contact with CZQX. Post flight reveals that the IRS mode knob had not been fully turned to the alignment detent during preflight in Europe.