Date: 201406
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: Learjet 45
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: VHF
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Captain; Pilot Not Flying; Check Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Communication Breakdown; Confusion; Distraction; Workload; Human-Machine Interface
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Aircraft Automation Overrode Flight Crew; Flight Crew FLC Overrode Automation; Flight Crew Became Reoriented; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

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.


Second narrative: When we got back to our home base; our Mechanic informed us that our Clearance Delivery radio head had malfunctioned and was causing our communication issues.The cause of this incident was an equipment malfunction combined with the crew losing track of the length of time between radio transmissions with ATC.The best way to prevent a future occurrence of this incident is to be vigilant about a periodic scan of the radios and especially confirm that the #2 radio is consistently tuned to 121.5.


Synopsis: 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.