Description

On April 25, 2006 a GENERAL ATOMICS AERONAUTICAL SYSTEMS Predator B/ MQ-9 Reaper an unmanned aerial vehicle (UAV)[1], collided with the terrain following a loss of engine power approximately 10 nautical miles northwest of the Nogales International Airport, Nogales, Arizona. The unmanned aircraft system was owned and operated by U.S. Customs and Border Protection (CBP). The flight was operating in night visual meteorological conditions (VMC) under instrument flight rules (IFR).

Synopsis

This is an extract from the factual accident report (CHI06MA121) published by the National Transportation Safety Board (NTSB), USA:

The flight was originally scheduled to take off at 1700 [all times referred in the Report are mountain standard times] given but was delayed because of the inability to establish a communication link between the UAV and PPO-1 [pilot payload operator - console 1] during initial power up. […]

The unmanned aerial systems normally are operated in such way to stay airborne for extended periods of time and more than one pilot is often scheduled to fly certain portions of each mission.

[…]The accident pilot reported that he took control of the flight at 1900 when [the UAV] was already airborne and operating in the temporary flight restriction (TFR) airspace. He reported that he flew from 1900 until 2100. At 2100, another pilot resumed control of the flight. The accident pilot took control of the flight again at 0300 and was scheduled to fly until 0500. He stated that the change-over briefing at 0300 was normal and that nothing had changed with the flight. […] Shortly after he resumed control of the flight, the lower monitor screen went blank on PPO-1. The screen then reappeared, but the telemetry (transmitted data) was locked up, so he decided to switch control of the UAS to PPO-2. The pilot stated that he informed the Border Patrol agent who was at PPO-2 that he needed to switch positions. The Border Patrol agent stated that he moved away from PPO-2 and left the GCS [ground control station]. The pilot stated that he verified the ignition was "hot" on PPO-2 and that the stability augmentation system was on. He reported that, at some point, he used his cell phone to call another pilot (who had been his instructor) to discuss what was going on.

The pilot stated that, after the switch to the PPO-2 console, he noticed that the UAV was not maintaining altitude, but he did not know why. He decided to shut down the ground data terminal (GDT) so that the UAV would begin its lost-link procedure. This procedure called for the UAV to autonomously climb to 15,000 feet above mean sea level (msl) and fly a predetermined course until contact could be reestablished. With no engine power, the UAV continued to descend below line-of-sight (LOS) communications, and further attempts to reestablish contact with the UAV were not successful.

Regarding the Unmanned Aerial Systems (UAS) operation protocols on the two nearly identical PPO consoles (PPO-1 and PPO-2), the Report further states:

Normally, a certified pilot controls the UAV from PPO-1, and the camera payload operator (typically a U.S. Border Patrol agent) controls the camera, which is mounted on the UAV, from PPO-2. Although the aircraft control levers (flaps, condition lever, throttle, and speed lever) on PPO-1 and PPO-2 appear identical, they may have different functions depending on which console controls the UAV. When PPO-1 controls the UAV, movement the condition lever to the forward position opens the fuel valve to the engine; movement to the middle position closes the fuel valve to the engine, which shuts down the engine; and movement to the aft position causes the propeller to feather. When the UAV is controlled by PPO-1, the condition lever at the PPO-2 console controls the camera's iris setting. Moving the lever forward increases the iris opening, moving the lever to the middle position locks the camera's iris setting, and moving the lever aft decreases the opening. Typically, the lever is set in the middle position. […]

Checklist procedures state that there should be pilots in both the PPO-1 and PPO-2 seats before switching control of the UAV from one PPO to the other. CBP stated that its procedures call for the avionics technician to assume the duties of a co-pilot for the purpose of assisting with the checklist items before switching control from one PPO to the other. This did not occur during the accident sequence.

The pilot stated that he did not use the checklist when making the switch. Checklist procedures state that before switching operational control between the two consoles, the pilot must match the control positions on the new console to those on the console that had been controlling the UAV. The pilot stated in an interview that he was in a "hurry" and that he failed to do this. The condition lever on PPO-2 was in the fuel cutoff position when the switch from PPO-1 to PPO-2 occurred. As a result, the fuel was cut off to the UAV engine when control was transferred to PPO-2. […]

There is an audible warning when an engine failure occurs. However, the same tone is used for every warning; the sound was not distinctive for a loss of engine power. The avionics technician stated that he heard the warning, but thought it was activating because they lost the Iridium satellite. In addition to the aural warning, the pilot should have seen a loss of torque and an exhaust gas temperature warning on the heads-down display.

The Communications/Air Traffic Control section (COA) of the report states that the air traffic services in Albuquerque Air Route Traffic Control Center (ZAB) were provided with mandatory training regarding the COA. The training consisted of a 30-minute briefing and PowerPoint presentation. Further in Communications/Radar section the Report states:

Both the ZAB controller and the OMIC [operations manager in charge] stated that they expected the UAS to fly the same course that it flew on several other lost-link events, which took it through a corridor just north of Nogales, Arizona, at 15,000 feet to a final recovery at FHU [Libby Army Airfield - from where the flight originated]. Following the loss of radar contact and radio communications, ATC (the ZAB controller) queried the UAV pilot regarding the location of the UAV. According to the controller, the UAV pilot did not know the location of the aircraft. While ATC considered the loss of radar contact and radio communications with UAV an emergency, neither the pilot nor ATC declared an emergency.

No causes to the accident nor safety recommendations are given in the Report.

Notes of the SKYbrary editor

1. ^ To ensure consistency with existing SKYbrary material the acronyms UAS (Unmanned Aerial Systems) and UAV (Unmanned Aerial Vehicle) are used in this article although in the original NTSB Report (CHI06MA121) the unpiloted aircraft is referred as UA (unmanned aircraft); The term UAS has emerged as successor to the earlier term UAV in recognition of the fact that a UAV itself is merely a part of the system which is required to operate the unmanned aircraft.

Related Articles

• LOC - Loss of Control;
• HF - Human Factors, Information Processing;

Further Reading

EASA

• EASA.2008.OP.08.: Interim Report of the Preliminary Impact Assessment on the Safety of Communication for Unmanned Aircraft Systems (UAS), by QinetiQ

NTSB

• NTSB Report CHI06MA121 on Investigation into the 2006 crash in Arizona USA, of US. Customs and Border Protection UAV Predator B;

Others

• Human Factors Analysis of a Predator B Crash, G. Carrigan et al, Humans and Automation Laboratory, MIT, USA.