Date: 202105
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: Light Transport
Operator: Fractional
Operating under: Part 135
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air/Ground Communication
Component problem: Failed
Reporter organization: Fractional
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We departed on a Class II international trip. The previous day (with a different Second in Command); we had tested the HF radios by receiving a time hack on the WWV atomic clock HF frequency. We had a good operations check and assumed the HF radios were working properly. The day of the trip; we again tested the HF by receiving a time hack on the ground; however; we could not transmit on the primary and secondary frequencies at the time due to our close proximity to the FBO hangars. After departing and prior to coast-out; the Second in Command (SIC) (also an experienced Captain who happens to have a lot of experience with HF in the military) attempted to test the HF radios using the Primary Frequency and a Secondary frequency while I flew the plane and managed the VHF radios. Prior to coast-out; the SIC determined that the HF radios were not transmitting. We reviewed the Operations Manual to make sure we were operating the HF radio properly and to make sure we weren't missing anything. We determined that we were operating it accordingly and that we had tried everything we could in order troubleshoot the problem. We briefly discussed our contingency options again prior to coast-out (including returning to our departure airport) and informed Center of the issue.  Center informed us that there was a flight right behind that we could relay our position with until we got back in radar contact. After that; there would be a southbound flight that was paralleling our course that would relay for us until we reached our destination.After discussing this with ZZZ Center; the controller also assured us that this was a legal option. We made radio contact with the relaying flight on the VHF air-to-air frequency. After we were confident we could continue to communicate and relay; the SIC and I again discussed our options and contingencies and we both elected to continue. We relayed our positions successfully until we reached ZZZ Center on VHF again. Our next contingency plan was that if we couldn't relay with another flight we would divert as ATC did not have any northbound traffic for us to relay with in order to return state-side. During this time; we briefed the passengers on the possibility of [diverting]. I transferred the controls to the SIC so that he could fly while I coordinated with ATC; relayed our position; plotted our course; and kept up with the NavLog in an effort to reduce each other's workload. He had worked hard attempting to troubleshoot the HF radios; meanwhile having me manage the radios and navigation allowed me to handle the lost HF event. Once talking to ZZZ Center; we made VHF contact with the southbound flight and we were confident that we could continue relaying position reports; we elected to continue to our destination via relay.We recorded each waypoint along the route on the NavLog and plotting chart; and successfully relayed each one. The other flight in turn would verify that each reporting point was received by ATC. Once we were within range of ATC; we contacted via VHF; they confirmed radar contact; we again exchanged the flight controls (I resumed pilot-flying duties and the SIC resumed pilot-monitoring duties) and we continued the rest of the way to our destination on VHF radios in the radar environment. The rest of the flight was uneventful. After deplaning our passengers at the destination; I called Maintenance Control to create a write-up and MEL the HF radios. The MEL restricted us to VHF communication. The log was completed and the MEL was complied with. My next call was to Operations to inform them of the issue and restrict the aircraft to 'Class 1 navigation only' until maintenance could fix the HF radios. The remainder of our scheduled trips were within radar service areas; so there were no additional operational issues concerning the HF radios and the MEL. As a side note; despite being a stressful situation; I believe the SIC (another Captain) and I handled the situation quite well all thingsconsidered. We communicated; risk assessed; and split duties effectively. If ATC hadn't assured us this was a legal option (it sounded like we weren't the first one to have this problem) or other flights had not been willing or able to help us relay our position; then we would have definitely had to have returned to our departure airport or diverted  after burning off a bunch of fuel to get the plane below landing weight.These HF radios probably have not been exercised in over a year due to COVID-19 international travel restrictions and lack of Class II flying. While we did test the HF the previous day by receiving a time hack; we did not check the transmit function of the HF radios. We checked the HF radios reception the previous day by receiving the time hack; however; we did not test the transmit function of the radio. Checking the transmitter the day before would have allowed us to MEL the HF earlier and prevent this trip from occurring on this tail number. Also I would recommend that as we continue to develop  training scenarios as part of our  recurrent training programs; that we include Class II navigation scenarios to supplement that training. In a normal year (without pandemic-level travel restrictions); we don't individually get to perform very many Class II trips. I believe including Class II training scenarios; including what to do during lost-comm events as well as other emergencies such as single-engine failure; depressurization; and medical emergencies); would be extremely beneficial in building decision-making processes in a Class II environment.


Second narrative: During the departure; I told the PIC that I would conduct the FMS navigation check and the HF check. The FMS navigation check was conducted almost immediately using a VOR.  The HF check was another story. On deck at departure airport; I was having issues getting a radio check on the ground with ZZZ Radio; but after discussing with maintenance; we collectively thought it was interference from the hangars right at the ramp.  An air check was required.  We could hear the HF clock on 10000 MHz but just could not raise ZZZ Radio.As the departure airport is very close to the ocean; we coasted out as I was attempting to get the HF to work.  Both HF radios seemed to be having a common issue with transmitting; this despite being able to hear intermittently HF traffic.  I was able to tune the radios but continued to fail in any contact with ZZZ Radio.  (HF1 seemed to not electronically tune as I pressed to transmit; HF2 seemed to tune pressing transmit; but no one could receive).  While the PIC flew the plane (and spoke with ATC); I continued to trouble shoot the radios exhausting all system knowledge.  We even pulled the manual out to make sure I was not missing anything.During my troubleshooting of the radios; the PIC was provided an option from ATC of relay with other aircraft.  Specifically; there was another aircraft very close by our position.  The other aircraft pilots agreed to take our HF relay if we needed that option.  At this point; I reported to the PIC that our HF radios were failed.  We were pretty much at the final fix prior to HF operations (20 minutes after takeoff). We both discussed the options prior to committing to the HF relay.  We could turn around and head back.  We could relay with other aircraft.  We could also pick up another relay that could take us all the way down (or perhaps back to ZZZ if we wanted that option).  We decided to continue with company to keep the flight going safely.  The clients were kept informed.  ATC was kept completely in the loop.As we entered radar control; ATC called to tell us that there were no northern flights that could help us get back but there was an Air Carrier flight which was willing to relay HF the remaining way.  Since the remaining oceanic airspace had 3 more fixes; we decided that this was a safe option allowing us to keep the mission on track.  With ATC facilitation; we contacted the flight while in radar control and established the link for our HF relay.  The HF relay with the Air Carrier took us into ATC airspace.  The rest of the flight was uneventful. Primarily; we both felt comfortable that we could continue to our destination safely. Secondly. This HF teaming; thanks to ATC; [and other flights] allowed our passengers to get to their destination with all the COVID restrictions compliances intact for their entry (a significant travel issue). Cause; aging equipment. I am not sure that this HF failure can be avoided.  Perhaps we need to do more checks of our equipment and keep them at a higher standard of repair and readiness.


Synopsis: Fractional jet crew reported their HF Radio did not work during a flight through non radar airspace so they relayed required position reports through other aircraft.