Date: 202110
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Large UAS; Fixed Wing
Operator: Commercial Operator (UAS)
Operating under: Public Aircraft Operations (UAS)
Flight plan: None
Mission: Surveying / Mapping (UAS)
Flight phase: Initial Approach; Landing
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Air/Ground Communication
Component problem: Malfunctioning
Reporter organization: Commercial Operator (UAS)
Reporter function: Person Manipulating Controls (UAS); Remote PIC (UAS)
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Remote Pilot (UAS); Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial; Flight Crew Flight Instructor
Human factors: Communication Breakdown; Confusion; Troubleshooting
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Ground Event / Encounter Ground Equipment Issue
Detector: Person Visual Observer (UAS)
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: During taxi; ZZZ Tower Controller asked us to fly a VFR pattern before we departed. We agreed; performed all checklists; took off; and were cleared for a right turnout to downwind; non-standard pattern altitude of 2;400 feet. We were also advised of traffic to follow; unmanned aircraft approaching base turn. We were told to 'extend your downwind; I'll call your base' from Tower; to which we read back instructions and continued on downwind. While passing mid-field; we heard the traffic in front of us call a base turn. Then we heard a chirp on the radios and then nothing. At a 2-mile perch point we called Tower with no response. At a 4-mile perch point we called Tower again and heard nothing. Shortly thereafter; our Visual Observer called us on his handheld radio saying 'Tower is trying to get a hold of you; they want you to turn base.' We turned base just inside of our approved airspace. At this point we determined we had a radio failure. As the Pilot In Command (PIC) I elected to break out of the specified pattern and proceed to our lost link orbit inside the Delta airspace; at which we would orbit and troubleshoot. I relayed this intent to our Visual Observer; who copied and reported he would relay to the Tower via his handheld radio. As we began our right turnout and headed to our emergency mission orbit; our technician found our radio issue and corrected it. As soon as our radios came back we heard multiple climb and descent instructions from Tower to multiple aircraft including our own. The first intelligible instruction we heard for us was to descend immediately to 1;500 feet. We elected to maintain our heading in our descent. After the descent; Tower moved other aircraft with respect to altitude and directed us to rejoin downwind for a full-stop landing in order to troubleshoot our radios. We informed Tower we had fixed our problem; requested a low approach to a right turnout for departure; and was cleared that. After the occurrence I contacted the Tower Controller to ask if I had incorrectly interpreted any procedures for radio failure in the specified pattern; (for example; wing rock up initial and break for a full stop). The Tower Controller checked the Letter of Agreement between [the] Airport and Company; and stated there were no defined procedures for NORDO UAS in the pattern. It is my opinion this was the primary contributing factor to this incident.

Callback: Reporter indicated a new procedure is now in place for lost communication.



Synopsis: A large fixed wing UAS remote pilot reported operating in the traffic pattern when they suffered a communication failure and no defined procedures were in place for a UAS suffering lost communications.