After about one hour of silence; a lr-45 crew attempted ATC communications and discovered a VHF syst...

Narrative:

We took off for a passenger flight. We departed VFR and picked up our IFR clearance with center out of 9;000 feet. We were given a clearance to 28;000 and routing around military airspace. Center handed us off to [another frequency] and upon contact we were cleared up to 40;000. The flight progressed normally with radio chatter that didn't seem out of the ordinary. Upon reaching the mountain range we started wondering why we hadn't been handed off to the next center and attempted to query center. We transmitted but got no answer. At that moment we observed that the number one radio tuning unit was on a frequency we didn't recognize. The number two radio tuning unit was no longer on 121.5. We tuned to 121.5 and transmitted and were given a frequency to contact center. The next center gave us a phone number for possible pilot deviation. At that time we were unaware of any problems with the aircraft and assumed we had missed a frequency. We were handed off to the next center; we contacted them and immediately lost contact again. Again we contacted 121.5 and were re-issued the frequency. At that time we observed our number one radio tuning unit cycling through random frequencies. We also observed our clearance delivery radio flashing a test pattern. Our number two radio tuning unit had switched from 121.5 to the secondary (flip-flop) position. During the remainder of the flight we had to monitor all three radio tuning units closely because they wouldn't stay on the frequencies that were set.this turned out to be a very insidious failure due to the fact that the radios didn't fail all together. We still heard normal radio traffic but were out of radio contact with our intended center for approximately one hour. Because the problem was discovered during a high work-load phase of flight it took a great deal of cockpit resources to recognize and manage the situation.there was a factor that affected the quality of crew performance. When a crew is given a phone number to call for a possible pilot deviation; it affects the crews focus on the task at hand. I personally think this is a lousy policy. There are enough resources available to the FAA for them to be able to contact the crew once they're safely on the ground. We were really beating ourselves up because until we realized there had been a failure of an aircraft system; we thought we were at fault for the loss of communication. It was an added drag on our performance and delayed our becoming aware that there was a systems failure and not a crew failure. Ultimately; it had an adverse impact on the safety of the flight. The only procedure I could come up with to recognize a failure like this in the future is to include in your scan; 121.5 still being in #2 primary. In our case it had moved to #2 secondary (flip-flop) and neither of us had caught it. You won't always (read; very rarely) remember the last center frequency but guard being in #2 primary is something that can be recognizable at a glance.

Original NASA ASRS Text

Title: After about one hour of silence; a LR-45 crew attempted ATC communications and discovered a VHF system malfunction which caused both radios to autotune random frequencies without the crew's input. Careful monitoring was then required.

Narrative: We took off for a passenger flight. We departed VFR and picked up our IFR clearance with Center out of 9;000 feet. We were given a clearance to 28;000 and routing around military airspace. Center handed us off to [another frequency] and upon contact we were cleared up to 40;000. The flight progressed normally with radio chatter that didn't seem out of the ordinary. Upon reaching the mountain range we started wondering why we hadn't been handed off to the next Center and attempted to query Center. We transmitted but got no answer. At that moment we observed that the number one radio tuning unit was on a frequency we didn't recognize. The number two radio tuning unit was no longer on 121.5. We tuned to 121.5 and transmitted and were given a frequency to contact Center. The next Center gave us a phone number for possible pilot deviation. At that time we were unaware of any problems with the aircraft and assumed we had missed a frequency. We were handed off to the next Center; we contacted them and immediately lost contact again. Again we contacted 121.5 and were re-issued the frequency. At that time we observed our number one radio tuning unit cycling through random frequencies. We also observed our clearance delivery radio flashing a test pattern. Our number two radio tuning unit had switched from 121.5 to the secondary (flip-flop) position. During the remainder of the flight we had to monitor all three radio tuning units closely because they wouldn't stay on the frequencies that were set.This turned out to be a very insidious failure due to the fact that the radios didn't fail all together. We still heard normal radio traffic but were out of radio contact with our intended Center for approximately one hour. Because the problem was discovered during a high work-load phase of flight it took a great deal of cockpit resources to recognize and manage the situation.There was a factor that affected the quality of crew performance. When a crew is given a phone number to call for a possible pilot deviation; it affects the crews focus on the task at hand. I personally think this is a lousy policy. There are enough resources available to the FAA for them to be able to contact the crew once they're safely on the ground. We were really beating ourselves up because until we realized there had been a failure of an aircraft system; we thought we were at fault for the loss of communication. It was an added drag on our performance and delayed our becoming aware that there was a systems failure and not a crew failure. Ultimately; it had an adverse impact on the safety of the flight. The only procedure I could come up with to recognize a failure like this in the future is to include in your scan; 121.5 still being in #2 primary. In our case it had moved to #2 secondary (flip-flop) and neither of us had caught it. You won't always (read; very rarely) remember the last Center frequency but Guard being in #2 primary is something that can be recognizable at a glance.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1180173
Time
Date	201406
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Learjet 45
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	VHF
Person 1
Function	Captain Pilot Not Flying Check Pilot
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 63 Flight Crew Total 6200 Flight Crew Type 2736
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 72 Flight Crew Total 9700 Flight Crew Type 2100
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

After about one hour of silence; a lr-45 crew attempted ATC communications and discovered a VHF system malfunction which caused both radios to autotune random frequencies without the crew's input. Careful monitoring was then required.