Safety

Operator error caused the 25 April crash of a US Customs and Border Patrol (CBP) General Atomics Predator B unmanned air vehicle, according to preliminary information from the US National Transportation Safety Board (NTSB). A failure to follow procedure when transferring control between operator consoles resulted in the UAV’s engine being shut down, and the Predator crashed near Nogales, Arizona (Flight International, 2-8 May).

The Predator ground control station has two almost-identical pilot payload operator (PPO) consoles. Normally, a certificated pilot controls the UAV from the PPO-1 console while the payload operator controls its onboard sensor from PPO-2. Both consoles have identical aircraft controls, including a stop/feather control for the Predator’s Honeywell TPE331 turboprop.

According to the NTSB, the mistake occurred when the PPO-1 console “locked up” and the pilot switched control to PPO-2. The checklist requires the pilot, before switching over, to match the control positions on the new console to those on the original console. The pilot failed to do this, says the NTSB. The stop/feather control on the PPO-2 console was in the fuel cut-off position when the switch-over occurred so the fuel was cut off to the UAV when control was transferred, says the NTSB.

Unaware the Predator’s engine had been shut down, the pilot “noticed the UAV was not maintaining altitude, but did not know why”, says the NTSB. He then shut down the ground control station so the Predator would enter its autonomous lost-link procedure, which calls for the UAV to climb to 15,000ft (4,600m) and fly a predetermined course until contact is re-established. Instead the Predator continued descending until it crashed in public land.