20010827029652A

(.19)On August 27, 2001, about 1840 hours pacific daylight time, tanker 87 , a Grumman TS-2A, N450DF, collided with tanker 92, a Grumman TS-2A, N442DF, near Hopland, California. The California department of forestry (cdf) was operating the airplanes as public-use fire suppression flights under the provisions of 14 CFR part 91. Tanker 87'S pilot held an airline transport pilot certificate; tanker 92'S pilot held an airline transport pilot certificate. The collision sequence and fire destroyed both airplanes. Tanker 92 departed ukiah at 1830, and tanker 87 departed at 1834. Visual meteorological conditions prevailed and no flight plans had been filed. The primary wreckage for tanker 87 was at coordinates 39 degrees 00.878 minutes north latitude and 123 degrees 11.603 minutes west longitude, at an estimated altitude of 1,955 feet. The primary wreckage for tanker 92 was at coordinates 39 degrees 01.089 minutes north latitude and 123 degrees 11.65 minutes west longitude, at an estimated altitude of 2,150 feet. Witnesses in tanker 21 reported that they checked in over lake mendocino. They fell in trail of tanker 87 as it left ukiah, and followed it in a southerly direction as they approached the fire. They observed a second tanker approach from the southeast. Tanker 21 was about 3,500 feet and looking below the horizon when they saw the two tankers collide. They observed tanker 87 continue in a southerly direction and the other tanker continue toward the west. A ground witness was on a promontory point observing the horizon to the west for signs of the fire. This observation point was about 1,900 feet elevation and 1 mile east of the accident site. This witness observed a tanker northwest of her position that was proceeding southbound on a track she had observed other tankers use during the day. As she looked back to the west, she observed another tanker south of her position that was proceeding in a westerly direction. She had not seen a tanker in this area during the day. She observed the tankers as they converged and collided. The westbound tanker went under the southbound tanker. She could see the top of goat rock (about 2,400 feet) above the two airplanes. Other ground witnesses were at the edge of a meadow in a saddle (about 2,000 feet elevation) between goat rock and bus mcgall peak (about 2,200 feet elevation and 1/2 mile southeast of goat rock). They observed a southbound tanker headed straight for them, and then observed the westbound tanker. The westbound tanker slid below the southbound tanker and a spherical cluster of debris emanated from the collision point, which was about 400 yards away on the opposite side of the meadow. The westbound tanker continued westbound and did not seem to have a tail. The southbound tanker continued toward them; they observed the tail of the southbound tanker separate. This airplane nosed over and exploded on ground contact about 200 feet from their location. They observed smoke coming from the direction of the other tanker. Several tanker pilots explained their normal operating procedures. An air observer (bus air for this fire) orbited the fire in a clockwise pattern about 2,000 AGL. This air observer remained in contact with the incident commander on the ground and directed the tanker drops on the fire. Bus air instructed the tankers on their drop order and described the desired target point for the drop. Bus air was not responsible for monitoring the tankers in their orbit. The tankers orbited in a counterclockwise pattern about 1,000 AGL. The first tankers on scene established a pattern altitude of 3,000 feet MSL, which bus air raised to 3,500 feet MSL by the end of the day. As tankers approached the scene they called 3 minutes out; if the frequency was congested they made a 2-minute or 1-minute call as appropriate. There was no established reporting or entry point, and a tanker could enter any point of the orbit from any direction. When bus air called in a tanker for a drop, that tanker would slide inside the orbit and descend as it setup for its drop. The dropping tanker pilot called downwind, base, and final turns before dropping his load at 200 feet AGL. The tanker pilot preparing to drop would focus on the inside of the pattern toward the fire. Bus air said three helicopters and eight tankers were working the fire. At the time of the accident, tankers 92, 86, and 91 were in orbit. Bus air would write down the tanker numbers as they called in 3 minutes out and usually ordered their drops in the same order as their check-in. A review of bus air's log recorded the sequence 86, 91, 21 (who checked in prior to reaching ukiah), and 92. Based on clock codes with 12 o'clock being north and the fire at the center, the tankers were in the following positions of the orbit when tanker 86 was called in to drop. Tanker 92 was at the 2 o'clock position; tanker 86 was at the 5 o'clock position; and tanker 91 was in the 9 o'clock position. Bus air's log indicated that tanker 92 was going to move up in sequence and follow tanker 86 in order to drop immediately after him in what the tanker crews call a daisy chain. The log did not contain an entry for tanker 87. As tanker 86 set up to enter the drop pattern, he heard tanker 92 say: "I've got you in sight; I'm going to swing wide." At this point, tanker 86 was south of bus mcgall peak and turning to the west about 2,500 MSL. During the left turn, the pilot of tanker 86 reached up to prepare his airplane for the drop. As he looked to his front right position, he observed the two airplanes collide. San joaquin helicopters provided the contract pilots for the tankers. Investigators from the safety board, cdf, and san joaquin helicopters examined the wreckage on scene. Tanker pilots reported that both propellers rotate clockwise as seen from the rear. The propeller blade tips were painted red; the propeller domes were painted black; and the leading edge of the engine cowling was painted black. The debris field encompassed an area about 1/2 mile in diameter. Investigators identified pieces from the upper forward cockpit area and propeller blade tips from the right propeller of tanker 92 commingled with various components of the tail section of tanker 87 in the area where witnesses reported that the collision occurred. This commingled area covered an area about 300 yards in diameter. The main wreckage for tanker 92 was about 400 yards west of this area, while the main wreckage for tanker 87 was about 400 yards south of this area. Cockpit pieces from tanker 92 included overhead hatches, the windscreen, and control levers located on the forward overhead section of the cockpit. These pieces were not charred. Components of the tail section of tanker 87 in the commingled debris field included the left horizontal stabilizer with the elevator attached. The fracture surface on this piece had structural members that bent and curled in an upward direction. Some segments exhibited red paint transfer marks. The remainder of the left horizontal stabilizer, the vertical stabilizer, the right horizontal stabilizer, and right elevator remained together and were about 50 yards from the separated left horizontal stabilizer piece. Both segments of the left horizontal stabilizer had fracture surfaces that were along a similar angle. This angle measured 33 degrees counterclockwise from the longitudinal axis as viewed from the rear. None of these components were charred. The two-segment rudder for tanker 87 fragmented into several pieces, which were scattered throughout the commingled debris field. All of these pieces were deformed, bent, and twisted with irregular fracture surfaces. Some of these pieces were covered with oil. One section exhibited a black paint transfer mark on its left side, which had dimensions similar to a propeller dome. This piece had another black paint transfer mark on its left side in the shape of an arc, which was similar in dimension and shape of an engine cowling. None of these components were charred. The debris field for the main wreckage of tanker 87 covered several hundred feet; all of the main wreckage and grass in this area was charred. Proceeding from an east to west direction, investigators identified the sonar area, wings, and landing gear, engines, propellers, bombay area, and cockpit area. Investigators accounted for the wing control surfaces in the main wreckage area. Major components for tanker 92 (including wings, engines, fuselage, and empennage) fragmented and separated, but were in their respective relative positions in the main wreckage. Sections of cockpit in the main wreckage included aft upper ceiling pieces and sections below the level of the windshield. The wings and engines were inverted and both wings exhibited similar leading edge crush damage that went aft to the main spar. Investigators accounted for the wing control surfaces in the main wreckage area. The empennage came to rest on its left side so that the right horizontal stabilizer was pointing up vertically. The vertical stabilizer and rudder exhibited aft and down crush damage. All components and vegetation in the main wreckage area were charred by fire. Several bombay doors and the nose gear separated and were within 40 yards of the main wreckage. The right propeller separated and came to rest about 150 yards downhill from the main wreckage; it was not charred. One of its blade tips was between the main wreckage and the propeller. This tip piece was leaning against a tree, which exhibited several debarked areas along its trunk. Gouges in the ground that were about 6 feet apart went downhill from this tip piece to the remainder of the propeller. The other two blade tips for the right engine were in the commingled debris field; these tips exhibited chordwise striations. Two blades remained attached to the left propeller. Only the gouged and deformed tip of its third blade was recovered. (-23) see NTSB report LAX01GA291B