SEA07TA181

The transport category airplane had been modified as a firefighting air tanker and was contracted to the State of California under an exclusive-use contract for the fire season. This was the second fire season for the operator, flight crew, and accident airplane. In order to facilitate the availability of the accident airplane, the contracting agency increased the personnel assigned to the program. Normal operational procedures required that a lead airplane fly the intended flight profile prior to the air tanker. The air tanker crew typically views the flight profile flown by the lead airplane, and then flies the profile while following the lead airplane. The lead airplane points out obstacles and general concerns along the flight path to the air tanker during that first flight. On the accident run, the original lead airplane with a pilot specifically trained for the DC-10 fire retardant drop procedures had switched out with a backup lead airplane and pilot in order to return to base for refueling purposes. The backup lead airplane flew the flight profile prior to the accident airplane joining the flight profile for the fire retardant drop. As the captain flew the profile, the accident airplane flew at a lower altitude than the lead airplane, entered a left turn, and impacted multiple trees with the left wing. The digital flight data recorder indicated that the airplane had entered a 35-degree left bank with a vertical acceleration from 0.8 to 1.4 G's, which is consistent with normal loading in a banked turn. Although the flight crew was experienced with the operation of the accident airplane, they had limited fire suppression experience. The operator provided training on the airplane and training in operating in the fire environment. The flight crew obtained the majority of their retardant drop experience (in excess of 100 hours using water for drops) during the certification testing for the airplane.

History of flight

On June 25, 2007, about 1720 Pacific daylight time, a McDonnell Douglas DC 10-10, N450AX (Tanker 910), impacted trees with the left wing during a fire suppression flight in support of the White Fire about 12 miles southwest of Tehachapi, California. The airplane was owned by BC Aircraft Leasing LLC, and leased to 10 Tanker Air Carrier, LLC. The California Department of Forestry and Fire Prevention (Cal Fire) was operating the airplane as a public use flight. The captain, first officer (FO), and flight engineer (FE), were not injured. The airplane was substantially damaged. Visual meteorological conditions prevailed, and Cal Fire flight tracking procedures were in effect. The airplane departed Southern California Logistics Airport, Victorville, California, at 1657.

According to Cal Fire personnel, the flight crew was preparing to jettison a load of retardant. While turning on final for the drop, the left wing impacted several trees. The flight crew climbed the airplane to 11,000 feet where they jettisoned the fire retardant. Then, they landed uneventfully at their departure airport at 1748.

Cal Fire had contracted with 10 Tanker Air Carrier, LLC to provide and operate the accident airplane. The airplane was to be operated on an exclusive use contract for wildland fire protection.

Thirteen impacted trees were identified by Cal Fire personnel. The first identified tree that sustained impact was 45 feet tall at a base elevation of 7,786 feet mean sea level (msl).

Personnel Statements

The flight crew submitted written statements regarding the accident. In summary, they indicated that they were conducting the third drop of the day. After joining with the lead airplane on the downwind leg for the retardant drop, they descended to about 7,700 feet msl. The run was set for a slight descent down the line of fire on a ridge. As they turned from base leg to final leg in a left turn of approximately 30 degrees, the airplane developed a sink rate, and the flight crew heard several thump sounds. The Captain verbalized the problem, advanced the throttles, and rolled the airplane's wings level. The Flight Engineer scanned the wing and noted damage to the left wing aileron, slat, and flap. The flight climbed and continued to a non-populated area with the lead airplane in trail. The fire retardant was jettisoned, the flight crew declared an emergency, and then they flew to Victorville where they landed uneventfully.

Lead Airplane Pilot Statement

The lead airplane pilot reported that he had worked with several air tankers the day of the accident. While transitioning to a fire, they heard the lead airplane for Tanker 910 was departing, and coordination was made for the change in lead airplanes. They later joined with Tanker 910, and briefed the crew on the altitude necessary to cross the ridgeline (7,700 feet with an altimeter set at 29.96 inches of Mercury), and the drop heading of 095 degrees. Tanker 910 trailed the lead airplane approximately 1 mile, and the lead airplane turned into the drop area and described the drop needed. They entered the traffic pattern, and Tanker 910 indicated that they were going to descend to 7,700 feet to which the pilot of the lead airplane concurred. As the lead airplane approached the ridgeline, the pilot gave a few additional short descriptions of the drop area and start point. The lead airplane pilot noted that there was no turbulence along the flight path. As the lead airplane pilot pulled up and clear of the ridgeline, he glanced back at Tanker 910 crossing the ridge. He felt that the airplane was at the appropriate altitude while crossing the ridge.

The lead airplane pilot then turned his head forward and heard Tanker 910, "make a call about sinking air and they had heard a thud noise." He continued around in a left turn to see the drop, and the flight crew indicated that they were going around. The lead airplane followed Tanker 910, and noted damage to the left wing. As Tanker 910 began the flight back to Victorville, the lead airplane pilot told the flight crew to jettison the retardant, but to do it slowly in the event that it caused a flight control malfunction. The retardant was jettisoned and both airplanes returned to Victorville.

Aircraft information

The McDonnell Douglas DC 10-10 airplane was modified for use in aerial fire fighting. The airplane is equipped with externally mounted tanks, capable of carrying up to 12,000 gallons of water or retardant. It was introduced into fire suppression service in 2006.

The aerial drop system is a computerized, gravity-feed system. The drop rate is controlled from the cockpit, and retardant is administered through the opening of the tank doors. At the time of the accident, the airplane was equipped with two drop buttons located between the captain and FO's seats; one button was for normal operations and the other was for emergency drops. According to 10 Tanker, a normal drop is initiated by the Captain, and carried out by the FO. Other aerial fire fighting aircraft are equipped with a drop/release button on the flying pilot's flight control yoke in the event that an immediate drop is necessary.

Flight recorders

The airplane was equipped with a digital flight data recorder (DFDR) and a cockpit voice recorder (CVR). The CVR had been overwritten and did not contain information pertinent to the accident flight.

The DFDR recorded that the accident flight was 51 minutes in duration. According to the recording, near the time of the accident, the airplane entered a left bank turn to 35 degrees, and the vertical acceleration varied between 0.8 and 1.2 Gs. Approximately 3 seconds prior to the initial tree impact, the vertical acceleration was 1.4 Gs, and the airplane was rolling from a 35 degree left bank to a 25 degree left bank. At the time of the initial tree impact, longitudinal acceleration was 0.3 G, and vertical acceleration was 1.0 G.

Additional information

Lead Airplane

Cal Fire personnel indicated that lead airplanes are used to assist tankers in the approach profile to the drop site. Lead airplane pilots are provided with more extensive training in low-level flight, and fire management. The lead airplane generally flies a profile run, and the tanker orbits while keeping constant view of the lead airplane. The tanker then joins the lead airplane and flies an identical profile of the lead airplane, while completing the retardant drop.

Cal Fire contracted with Dyn Corp to provide a lead airplane for the DC-10. The purpose of a lead airplane was to provide a visual pathway for the fire tanker to fly during the mission. Both pilots hired by Dyn Corp were former United States Forest Service (USFS) lead airplane pilots and instructors. As a backup, the Bureau of Land Management (BLM) offered their lead airplane that was based at William H. Fox Field, Lancaster, California. The BLM pilot was given training in lead airplane operations for the DC-10.

According to Cal Fire, during the accident flight, the contract airplane with Dyn Corp needed additional fuel and departed the area. The BLM airplane flew the lead airplane position during the accident. The BLM pilot flew the retardant drop profile prior to the DC-10 joining the approach sequence. As the BLM pilot flew the drop path for the second time, the DC-10 followed. During the approach, the DC-10 was below the altitude of the lead airplane's flight path.

Cal Fire Training Program

According to Cal Fire personnel, the DC-10 program was developed similar to other programs using large aircraft with a removable retardant delivery system installed. In these systems, the crews of these airplanes undergo a familiarization program, but they are not trained fire pilots, and do not operate without the coordination and assistance of a lead airplane.

In July of 2006, Cal Fire personnel evaluated the feasibi