Narrative:

I received normal departure and routing instructions via a filed IFR flight plan. The departure and progression to cruise were routine. Near bishop; nv; I was advised by ATC to expect routing changes and the possible loss of GPS. Listening to other pilots in the area they confirmed that GPS would eventually not be available. I then began to transition from my GPS navigation to a VOR based system. During this transition; ATC again called with the new routing. Also at this point; ATC radio transmissions started to become difficult to clearly hear and comprehend (something I advised them of). I wrote down the clearance as I heard it and was proceeding to lidat; J92 at boger city (bgd); a VOR just north of amarillo. I either asked for or the controller offered clarification (again garbled). This time I understood them to say '...after lidat; beaty; J92 (garbled); direct boger city (bgd).' what I understand from the second transmission was she changing the assignment to proceed to 'btv' then 'direct boger;' eliminate the J92 instruction (which made more sense). In retrospect; I believe she meant; after lidat proceed to bty; then J92 to boulder city (bld) then direct to ama. Her use of the term 'direct' after J92 was confusing. Obviously the terms 'boulder' and 'boger' are very similar and easy to transpose even with good communication clarity. This is what I did and assumed that is what she wanted me to do. During the entire sequence I was attempting to transition from GPS to VOR based navigation. To be honest VOR is not something I use very often. I was therefore in the process of getting out the maps; finding my current location; dialing the frequencies and adjusting the heading indicators. With in a very short span the GPS did infact stopped working. All three units went blank becoming just warning screens. No maps were displayed. Significantly there was no warning as would have normally been the case of an impending restricted area ahead. With no GPS map there as no quick way to determine I was headed at a restricted area. I discovered this only upon ATC's final amendment to my routing and giving me vectors. I have always been meticulous about not flying into any form of restricted area. I follow ATC instructions to the best of my ability. I sincerely regret this incident. I will get more up to date and prepared to fly in the VOR based navigational system. I would also hope that ATC would give a pilot an earlier warning and more time to adjust when faced with a similar situation. The few minutes I had were not adequate for me to get out the materials necessary to locate and after my navigational mode. I will also in the future I will better scrutinize any transmission from ATC; confirm not only the instructions but intent and not rely on partial understanding of a scratch radio communication. I will also attempt to be more attune to potential confusion between similar sounding named 'boulder and boger' as an example.

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Original NASA ASRS Text

Title: A business aircraft pilot at FL250 near BTY misunderstood his ATC clearance as a planned GPS system outage occurred and did not transition to VOR airways quickly enough which allowed his aircraft to penetrate restricted airspace.

Narrative: I received normal departure and routing instructions via a filed IFR flight plan. The departure and progression to cruise were routine. Near Bishop; NV; I was advised by ATC to expect routing changes and the possible loss of GPS. Listening to other pilots in the area they confirmed that GPS would eventually not be available. I then began to transition from my GPS navigation to a VOR based system. During this transition; ATC again called with the new routing. Also at this point; ATC radio transmissions started to become difficult to clearly hear and comprehend (something I advised them of). I wrote down the clearance as I heard it and was proceeding to Lidat; J92 at Boger City (BGD); a VOR just north of Amarillo. I either asked for or the Controller offered clarification (again garbled). This time I understood them to say '...after Lidat; Beaty; J92 (garbled); direct Boger City (BGD).' What I understand from the second transmission was she changing the assignment to proceed to 'BTV' then 'direct Boger;' eliminate the J92 instruction (which made more sense). In retrospect; I believe she meant; after Lidat proceed to BTY; then J92 to Boulder City (BLD) then direct to AMA. Her use of the term 'direct' after J92 was confusing. Obviously the terms 'Boulder' and 'Boger' are very similar and easy to transpose even with good communication clarity. This is what I did and assumed that is what she wanted me to do. During the entire sequence I was attempting to transition from GPS to VOR based navigation. To be honest VOR is not something I use very often. I was therefore in the process of getting out the maps; finding my current location; dialing the frequencies and adjusting the heading indicators. With in a very short span the GPS did infact stopped working. All three units went blank becoming just warning screens. No maps were displayed. Significantly there was no warning as would have normally been the case of an impending restricted area ahead. With no GPS map there as no quick way to determine I was headed at a restricted area. I discovered this only upon ATC's final amendment to my routing and giving me vectors. I have always been meticulous about not flying into any form of restricted area. I follow ATC instructions to the best of my ability. I sincerely regret this incident. I will get more up to date and prepared to fly in the VOR based navigational system. I would also hope that ATC would give a pilot an earlier warning and more time to adjust when faced with a similar situation. The few minutes I had were not adequate for me to get out the materials necessary to locate and after my navigational mode. I will also in the future I will better scrutinize any transmission from ATC; confirm not only the instructions but intent and not rely on partial understanding of a scratch radio communication. I will also attempt to be more attune to potential confusion between similar sounding named 'Boulder and Boger' as an example.

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.