Date: 201203
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Twin Otter DHC-6
Flight plan: VFR
Flight phase: Landing
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Government
Reporter function: Ground; Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Vehicle; Ground Incursion Runway
Detector: Person Air Traffic Control
Result: General None Reported / Taken
Contributing factors: Human Factors; Procedure; Equipment / Tooling
Primary problem: Human Factors

Narrative: I was working Local Control 1; Local Control 2 and Ground Control. Traffic was very light and weather was VFR. An airport vehicle called on Ground Control frequency on the south ramp requesting to proceed southbound on Taxiway Papa to Echo. I instructed the airport vehicle to 'proceed as requested Taxiway Papa'. The airport vehicle did not read back this instruction and proceed from the south ramp southbound on Taxiway Papa to Taxiway Echo. The airport vehicle called me on Ground frequency with a radio check. I told the airport vehicle 'I have you loud and clear; how me.' I got no radio check response from the airport vehicle. The following transmission was the airport vehicle telling me I was 'very hard to read' and that he was 'switching over to air'. My thought was he was going to attempt contact on my Local Control frequency. A few seconds after I attempted a radio check with the airport vehicle on local control. The airport vehicle did not respond to the radio check. Instead the airport vehicle requested 'Airport vehicle permission to enter on runway three twenty-one full access.' I responded; 'Airport vehicle; hold short Runway Two One; landing traffic.' At this time I observed the airport vehicle proceeded past the hold short line on Taxiway Echo onto the runway as a DHC6 was executing landing roll. The airport vehicle next transmission was inaudible. The airport vehicle's next transmission; 'Airport vehicle may be having radio issues.' Airport vehicle's next transmission; 'Copy airport vehicle; copy that you gave me permission.' I then gave the DHC6 taxi instructions to parking via Taxiway Delta and Taxiway Papa. The airport vehicle attempted a radio check on Ground; 'ATC ground airport vehicle radio check on Ground.' I responded; 'Airport vehicle ATC Ground radio check how do you hear.' I made another attempt; 'Airport vehicle radio check how do you hear me.' The airport vehicle responded; 'Airport vehicle to Tower you were garbled right now....can I have permission to head over to the RF station cross Papa Taxiway from Echo.' I responded;' Airport vehicle; ATC Ground proceed to the RF station via Taxiway Papa; report off.' I did not get a response so I told the airport vehicle to 'look for the light gun'. The airport vehicle then said; 'ATC Ground airport vehicle in the blind I'm clear of Papa Taxiway. My recommendations for this scenario would be to the employees in the vehicles as well as controllers. ENSURE you have established communication with Tower PRIOR to entering an active runway. The airport vehicle was aware of radio problems and yet still proceeded on the runway. As a vehicle if you feel your transmission from the Tower was 'garbled' or 'very hard to read' your vehicle should NOT be moving! I also make a recommendation to get a read back from the vehicle after initial call up. When I told the airport vehicle to proceed as requested; I did not get a read back nor did I request one. In the future I will request read backs from all vehicles requesting to enter taxiways; runways and other movement areas to ensure runway and taxiway integrity is maintained at all times.




Synopsis: Tower Controller provided a detailed account of a airport operations vehicle experiencing radio equipment problems while operating on and near an active runway.