Narrative:

I was the pilot not flying; repositioning without passengers to las. After passing the bih VOR we were cleared direct to the lidat intersection; then to join J92 bty and the fuzzy 7 arrival; bty transition to las. A couple minutes prior to the lidat intersection 3 F/a 18 fighters flew beneath us; as the the PF and I were commenting on the fighters our aircraft began rolling slightly side to side as if hunting for a direction to fly. We immediately noticed annunciations on the universal FMS; trimble GPS and the instrument panel. We then checked the FMS message page; it said 'position uncertain.' then we checked the FMS data page for GPS signal. It said 'aqp' acquiring signal. We then went to the GPS satellite page; it said 'no satellites in view.' I then tuned in the bty VOR frequency 114.7 and selected the 310 degree radial; 120 degree inbound; to bty. At exactly that moment ATC asked if we were assigned a heading. We replied 'no; we were cleared direct lidat and the fuzzy 7 arrival.' the controller instructed us to turn direct bty; however our FMS regained its GPS signal and had already begun the turn to intercept J92 direct bty. We observed that we had passed and were to the left of the airway centerline; however we did not have a full scale deflection. The event began with a momentary loss or interruption of our GPS satellite signal causing our aircraft FMS to revert to a 'dr' dead reckoning mode. In this mode we lost our FMS 'smart turn' function causing our turn to begin after crossing the lidat intersection. A contributing factor was our ground speed of approximately 450 kts and a nearly 90 degree turn to intercept J92. At that ground speed; and nearly a 90 degree turn; our 'smart turn' function should begin the turn prior to the lidat intersection approximately 6 to 7 miles without ever over flying lidat. The late turn caused us to brush the restricted zone on the immediate edge of the airway. A los angeles ATC center controller during a similar event while approaching the dag VOR said on the radio that 'multiple aircraft on that day were experiencing similar loss or interruptions of GPS satellite signal due to china lake naval air center activities.' it should also be noted that china lake naval air station tests GPS 'jammers' installed on F/a 18 fighter aircraft. This may or may not have had any bearing on our momentary loss of GPS satellite signal on our flight to las. However; those exact type of fighter aircraft were flying out of the china lake naval air station restricted airspace from our right side flying north bound just underneath us on that day seconds prior to us noticing the loss of GPS signal. Listed below are some contributing factors and some steps that we will take to prevent further events: 1. While our aircraft are equipped with dual independent long range navigation units; we will use the right side HSI with VOR radials selected as a back up in the event of a momentary loss of GPS signal 2. We will monitor FMS 'smart turn' functions prior to crossing any fix bordering airspace or obstacles that could adversely affect our flight 3. We were cleared direct to the lidat intersection; as cleared; had we flown over the intersection at that speed and with the degree of turn required to join J92 there is no way at a standard rate turn to avoid entering restricted airspace. Had there been a lead radial or transition zone on the other side of the lidat intersection this would not have occurred. 4. Had our clearance been to fly present heading towards the lidat intersection and intercept J92; this would not have occurred 5. The reliance on automation during a critical phase of flight in an area bordered by restricted zones was a contributing factor.

Google
 

Original NASA ASRS Text

Title: A corporate jet First Officer described temporarily losing the GPS signal on arrival into LAS and speculated that it might have been due to GPS jamming activities.

Narrative: I was the Pilot Not Flying; repositioning without passengers to LAS. After passing the BIH VOR we were cleared direct to the LIDAT intersection; then to join J92 BTY and the FUZZY 7 arrival; BTY transition to LAS. A couple minutes prior to the LIDAT Intersection 3 F/A 18 Fighters flew beneath us; as the the PF and I were commenting on the fighters our aircraft began rolling slightly side to side as if hunting for a direction to fly. We immediately noticed annunciations on the Universal FMS; Trimble GPS and the instrument panel. We then checked the FMS MSG page; it said 'position uncertain.' Then we checked the FMS Data page for GPS signal. It said 'AQP' acquiring signal. We then went to the GPS satellite page; it said 'no satellites in view.' I then tuned in the BTY VOR frequency 114.7 and selected the 310 degree radial; 120 degree inbound; to BTY. At exactly that moment ATC asked if we were assigned a heading. We replied 'no; we were cleared direct LIDAT and the FUZZY 7 arrival.' The controller instructed us to turn direct BTY; however our FMS regained its GPS signal and had already begun the turn to intercept J92 direct BTY. We observed that we had passed and were to the left of the airway centerline; however we did not have a full scale deflection. The event began with a momentary loss or interruption of our GPS satellite signal causing our aircraft FMS to revert to a 'DR' dead reckoning mode. In this mode we lost our FMS 'smart turn' function causing our turn to begin after crossing the LIDAT intersection. A contributing factor was our ground speed of approximately 450 kts and a nearly 90 degree turn to intercept J92. At that ground speed; and nearly a 90 degree turn; our 'smart turn' function should begin the turn prior to the LIDAT intersection approximately 6 to 7 miles without ever over flying LIDAT. The late turn caused us to brush the restricted zone on the immediate edge of the airway. A Los Angeles ATC Center Controller during a similar event while approaching the DAG VOR said on the radio that 'multiple aircraft on that day were experiencing similar loss or interruptions of GPS satellite signal due to China Lake Naval Air Center activities.' It should also be noted that China Lake Naval Air Station tests GPS 'jammers' installed on F/A 18 fighter aircraft. This may or may not have had any bearing on our momentary loss of GPS satellite signal on our flight to LAS. However; those exact type of fighter aircraft were flying out of the China Lake Naval Air Station restricted airspace from our right side flying north bound just underneath us on that day seconds prior to us noticing the loss of GPS signal. Listed below are some contributing factors and some steps that we will take to prevent further events: 1. While our aircraft are equipped with dual independent long range navigation units; we will use the right side HSI with VOR radials selected as a back up in the event of a momentary loss of GPS signal 2. We will monitor FMS 'smart turn' functions prior to crossing any fix bordering airspace or obstacles that could adversely affect our flight 3. We were cleared direct to the LIDAT intersection; as cleared; had we flown over the intersection at that speed and with the degree of turn required to join J92 there is no way at a standard rate turn to avoid entering restricted airspace. Had there been a lead radial or transition zone on the other side of the LIDAT intersection this would not have occurred. 4. Had our clearance been to fly present heading towards the LIDAT intersection and intercept J92; this would not have occurred 5. The reliance on automation during a critical phase of flight in an area bordered by restricted zones was a contributing factor.

Data retrieved from NASA's ASRS site as of April 2012 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.