N416DF

HISTORY OF FLIGHT

On October 5, 1998, at 1236 hours Pacific daylight time, a Grumman TS-2A, N416DF, operated under 14 CFR Part 91 by the California Department of Forestry (CDF) as Tanker 96, was destroyed during a collision with mountainous terrain near Banning, California. The government owned aircraft was maintained and pilot services provided by San Joaquin Helicopters (SJH), a private contractor. The pilot was fatally injured. Visual meteorological conditions prevailed for the flight. The aircraft was on a fire suppression mission at the time of the accident and carrying fire retardant chemicals.

According to the CDF, the tanker pilot made two previous drops on the Mt. Edna fire line. The tanker pilots are directed by spotter aircraft orbiting the fire. The accident pilot was directed by the spotter aircraft to tag onto the previous drop of Tanker 75.

According to the pilot of Tanker 75, he had dropped in the same area, but in the opposite direction due to a gap between the previous drop and the rest of the line they were attempting to build. He stated that the drop was basically into the wind and he encountered severe turbulence but no loss of flight control. However, he had experienced a momentary loss of control on the previous drop while orbiting the fire approximately 1,000 feet agl and 1/4 mile west of the accident site in a left bank (approximately 15 degrees). The aircraft rolled 45-60 degrees. He concluded that there was a severe "rotor" effect coming off the ridges on the east side of the fire.

Another tanker pilot and an U.S. Forest Service (USFS) spotter pilot witnessed the approach to the drop area. They reported that the pilot was turning from base leg to the westerly drop heading while in a 60-degree left bank. The aircraft suddenly rolled further left to 90 degrees, at which point the left wing tip struck the terrain prior to releasing retardant. According to the CDF Aviation Management, the minimum approved descent altitude for a retardant drop is 150 feet above vegetation/terrain.

Pilots and ground personnel estimated the winds to be 25 to 30 mph with gusts of 40 mph from the east. One pilot called the estimate conservative. They also reported turbulence and bad air. Airmet Tango had been issued for turbulence and isolated severe conditions mainly below 10,000 in vicinity of canyons and passes.

The aircraft was based at Fresno, California. The pilot had flown from Fresno to the Mt. Edna fire site with retardant on the morning of the accident. After the initial drop, he landed at Hemet-Ryan Airport, reloaded with retardant, and dispensed the load on the fire line. On the last drop, he reloaded, refueled, and departed at 1229 and crashed at 1236. The combined totals of flight time for the pilot on the day of the accident was about 2:42 hours.

PERSONNEL INFORMATION

San Joaquin Helicopters employed the airline transport rated pilot as a seasonal employee who had flown three fire seasons with them. The pilot had also flown numerous seasons with other contractors as a tanker pilot. He was type rated in 11 heavy aircraft and 4 additional with VFR limitations. At the start of the 1998 fire season he reported 16,680 total flight hours, with 865 hours in the TS-2A aircraft. He also reported 2,970 hours as a tanker pilot.

On December 16, 1997, the pilot was issued a first-class medical certificate with restrictions that he wear glasses for distant vision and possess glasses for near vision.

At the beginning of the April 30, 1998 season, the pilot was given a pilot proficiency evaluation that consisted of an oral evaluation of aircraft systems, limitations, normal and emergency procedures, and fire-fighting mission questions. Also addressed were ground operation issues for aircraft flight log, preflight, checklist, taxi technique, and takeoff computations. The pilot was evaluated during an actual flight of 40 minutes. The details of the total evaluation are attached to this report.

On September 21, 1998, at the Fresno Air Attack Base the pilot satisfactorily completed a PIC proficiency check and instrument training under the provisions of 14 CFR 61.57. He also demonstrated the skill and knowledge requirements as required by 14 CFR Part 137.19.

The pilot was on a normal day-off schedule the day before the accident. The day of the accident his day started about 0800. Prior to departing Fresno at 0912, he flew a proficiency flight of 12 minutes. At the time of the accident he had been on duty about 4:36 hours. According to contract #7CA51199 part four, section K, 4.7.4 Flight time in state-owned aircraft: Flight time shall not exceed a total of 7 hours per day.

AIRCRAFT INFORMATION

The ex-military aircraft was made available from long term storage to the California Department of Forestry and Fire Protection for Forest and Wildlife Conservation. The Federal Aviation Administration (FAA) issued a Special Airworthiness Certificate in the restricted category on June 20, 1985. The operating limitations specify, in part:

. . . no person may operate this aircraft for other than the purpose for which the special airworthiness certificate was issued (Forest and Wildlife Conservation) and in accordance with operating limitations contained in FAR 91.313 with special operating limitations to operate over densely populated areas, in congested airways, from busy airports where passenger transport operations are being conducted and those contained herein . . . .

Maintenance was provided by the contractor, San Joaquin Helicopters, under 14 CFR 91.409 (F), a continuous airworthiness program. The aircraft flight hours and maintenance data reflected in this report were obtained from the CDF Aviation Management. According to the maintenance contractor inspection schedule, the last annual inspection was performed on April 14, 1998, at 10,676.4 hours. A 100-hour inspection was conducted on July 31, 1998, at 10,776.4 hours.

The annual inspection of the aircraft is routinely performed by SJH during the winter months after the fire season. Prior to the aircraft going back on-line for a fire season, the CDF performs a 27 page S-2 Operations Acceptance Check. A copy of the detailed check is included in this report.

The aircraft was refueled with 357.8 gallons (full fuel) of 100LL aviation fuel after repositioning from Fresno to the Mt. Edna fire, dispensing a load of retardant, and landing at Hemet.

Preliminary Stall Speed vs Angle of Bank calculations were made using the NAVAIR 01-85SAA-1 operations manual and estimating the weight to be 25,876 pounds. A 60-degree bank could generate a stall at 94 knots; a 70-degree bank could generate a stall at 110 knots. The accident site density altitude was estimated about 6,600 feet.

At the time of the accident the aircraft had accumulated 10,848.7 total flight hours. On the day of the accident the pilot flew the aircraft .2 hours for proficiency prior to departing for Hemet. The flight time from Fresno to Hemet was 1:35 hours. The aircraft performed two retardant drops from the Hemet base. The combined flight totals for the day were 2:42 hours.

The aircraft was fitted with an 800-gallon Aero Union Corporation Grumman S-2 retardant tank system. The doors are opened and closed by hydraulic actuators controlled electrically through a relay system. The airplane's 1,500 p.s.i. hydraulic system supplies the energy.

On March 15, 1999, the Safety Board visited the CDF facilities located at Mather, California. A pilot generated test procedure similar to the Aero Union procedure for the retardant tank operational systems was discussed and examined. A brief functional test of a tanker door system was performed.

On March 16, 1999, Tanker's T-100 and T-93 retardant tank operating systems were ground tested in all modes with the engines running. The tests following the written procedures met the required checks. Tanker T-100 experienced a sticking microswitch on the No. 3 door open light limit switch.

The drop/release button is located on the left side of the pilot's control yoke next to the microphone button and is recessed into a circular ring. Improper/interrupted use of the release button was found to cause a door release interruption. The Aero Union operational manual calls for the switch to be held for 1 full second without interruption.

The system has four doors which may be opened individually, or in any combination of openings either manually or automatically. The drop system control, warning, and condition advisory device panel is located on the lower portion of the center instrument panel.

The switch has two positions "ARM" and "OFF" and is switch guarded in the arm position. The point at which the system is actually "ARMED" for a drop is pilot preference. Some pilots prefer to "ARM" at takeoff to prevent forgetting.

An emergency pneumatic tank dump system is provided utilizing a nitrogen charged accumulator. A red emergency dump button is located on the center of the instrument and must be held "momentarily."

METEOROLOGICAL INFORMATION

There are no official weather observations available that are representative of the accident area. Pilot estimates of wind conditions were 25 to 30 mph with gusts of 40 plus from the east.

At 1246, Beaumont, which is located about 8 miles northwest of the accident site, was reporting: wind 090 degrees at 15 knots with gusts to 26 knots; visibility 25 miles; temperature 70 degrees Fahrenheit; dew point 28 degrees Fahrenheit; and smoke was reported in the vicinity.

At 1153, Riverside Arlington Airport, located about 32 miles west of the accident site, was reporting: clear with visibility 10 miles; temperature 82 degrees Fahrenheit; dew point 32 degrees Fahrenheit; wind direction 030 degrees at 18 knots with gusts of 25 knots; altimeter 30.01 inHg.

Airmet Tango, a weather advisory, was valid for the time period and reported: from 40 southwest of...