N4995G – Sikorsky (Lockheed Martin) S-58 – 1994-01-28 NTSB Accident Report

History of the Flight

On January 28, 1994, about 0737 hours Pacific standard time, a Sikorsky S58-JT, N4995G, crashed on a high-rise building during an external load operation at San Jose, California. The helicopter was being operated as a visual flight rules (VFR) local flight under Title 14 CFR Part 133 when the accident occurred. The helicopter, registered to and operated by Air One Helicopters Inc., San Jose, California, was destroyed by impact and postimpact fire. The certificated airline transport pilot, the sole occupant, received fatal injuries. Visual meteorological conditions prevailed. The flight originated at the San Jose International Airport about 0722 hours.

The operator reported that the helicopter was being utilized to remove a large cooling tower fan from the top of a 13-floor building located in the business district of the city. The pilot contacted the ground controller at the San Jose Air Traffic Control Tower (ATCT) at 0720:18 hours and requested permission to taxi for takeoff. At 0722:05 hours, the aircraft was cleared for departure by the local controller and at 0724:08 hours, the pilot reported as "on station". The building is located about 1 1/2 miles southeast of the airport.

A three-man ground crew from the helicopter operator and an air conditioning company were assigned to the operation. A helicopter company employee, a member of the ground crew, reported that the helicopter was originally going to land in the west parking lot of the building to attach a 100-foot Kevlar lifting cable to the belly of the aircraft; however, the landing area was restricted by numerous light poles. The crew member attached the cable to the helicopter while it was at a hover over the top of the building. The crew disassembled a portion of the cooling tower and the helicopter successfully removed a large fan to the ground level parking lot. The helicopter then deposited a 1,800-pound steam cleaning machine on the roof, adjacent to the tower.

The crew on the building unhooked the machine from the lifting cable and was preparing to unhook the cable from the helicopter. As the helicopter was at a 100-foot hover above the building, the crew heard the engine sounds decrease and observed the main rotor blades begin to slow. The helicopter then descended vertically onto the top of a two-level central core penthouse building that housed elevator, boiler, and air-conditioning machinery. After contacting the penthouse roof, the helicopter began to roll onto its right side.

The main rotor blades contacted the building parapet wall and separated near the inboard ends of the blades. A postcrash fire erupted and the crew attempted to fight the fire with hand extinguishers. The crew indicated that during the impact the vertical tail section of the fuselage separated. After the helicopter came to rest, the main rotor blade roots still attached to the mast were still turning and they could hear the engines still spooling down and then stop completely. The crew was not injured and no persons on the ground level were injured. At 0737:12 hours, a pilot reported the fire on the roof of the building to the San Jose ATCT.

A Federal Aviation Administration (FAA) operations inspector, San Jose Flight Standards District Office (FSDO), was observing the lifting operation from the ground-level west parking lot to monitor the flight's compliance with a 14 CFR Part 133 external load plan. He reported that the helicopter was facing toward the west while hovering above the roof and heard the sound of the engine(s) spooling down. The helicopter nose pitched down about 5 degrees and descended vertically without any fuselage yaw. The main rotor blades began slowing down and the helicopter descended out of view. Portions of the main rotor blades fell away from the roof top into the parking lot. The inspector observed smoke and fire about 5 seconds after the crash.

Numerous ground witnesses also reported hearing the engine sounds decrease and the main rotor blades slowing down. The initial fire started as a small flame near the cabin area that quickly spread, engulfing the helicopter. The witnesses reported seeing extremely bright sparks emanating from the fire.

The accident occurred during the hours of daylight at attitude 37 degrees, 20.91 minutes north and longitude 121 degrees 54.08 minutes west.

Other Damage

The building received impact and fire damage to the penthouse building and exterior of the roof area. In addition, several upper floors of the building received water damage.

Crew Information

The pilot held an airline transport pilot certificate with a rotorcraft helicopter rating, and type ratings in Bell 206 and Sikorsky S58 aircraft. He held commercial pilot privileges with a single-engine land rating. In addition, the pilot held a flight instructor certificate with a rotorcraft helicopter rating. He also held a mechanics certificate with airframe and powerplant ratings. The most recent second-class medical certificate was issued to the pilot on August 19, 1993, and contained no limitations.

No personal flight records were located for the pilot and the aeronautical experience listed on page 6 of this report was obtained from a review of the airmen FAA records on file in the Airman and Medical Records Center located in Oklahoma City. In addition, information was obtained from a review of records maintained by the operator.

According to the information entered on the pilot's application for medical certificate dated August 19, 1994, his total aeronautical experience consisted of 7,000 hours. The operator reported that the pilot had accrued 6,200 hours in helicopters and 1,500 hours in the accident aircraft make and model. In the preceding 90 and 30 days prior to the accident, the report lists a total of 43 and 19 hours, respectively, flown. The operator provided an undated letter from the San Jose FSDO indicating that the pilot was qualified as serve as pilot-in-command in external load operations.

The chief pilot reported that the pilot received annual recurrent training, including a check ride, for 14 CFR Part 135 operations. The company does not conduct (nor is one required under Part 133) ground or flight training in external load operations. Since external loads are constantly being conducted, the accident pilot was routinely observed by ground personnel including the chief pilot. The ground crew indicated that no mission briefing was conducted prior to the accident flight.

Aircraft Information

The accident aircraft is equipped with twin Pratt and Whitney PT-6T engines that provide independent power to a combining gearbox. The gearbox drives a single output shaft connected to an angle gearbox, which provides power input to the main rotor transmission. The aircraft is certified as a single-engine helicopter.

The recording hour meter in the aircraft was destroyed. Prior to departure on the accident flight, the aircraft maintenance log sheet indicated that the helicopter had accumulated a total time in service of 8,523.8 flight hours. The helicopter was utilized almost exclusively for external load operations and was maintained according to the manufacturers' inspection program. Examination of the maintenance records revealed that the most recent Phase III inspection was accomplished on August 8, 1993, 47.4 hours before the accident. The left engine had accrued a total time in service of 6,456 hours of operation. The maintenance records note that a major overhaul was accomplished on February 5, 1980, 2,927.5 hours of operation before the accident.

The right engine had accrued a total time in service of 5,661.7 hours of operation. The engine was overhauled on September 10, 1984, 2,206.7 hours before the accident.

The combining gearbox had accrued a total time in service of 5,747.6 hours of operation. The gearbox was overhauled on November 21, 1983, 2,778.1 hours before the accident.

Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the aircraft prior to departure.

The aircraft fuel system consists of a forward and aft tank. The forward tank is partitioned into six cells. The aft tank consists of two interconnected tanks partitioned into three cells each. The left engine is supplied by the forward tank and the right engine from the aft. Each engine has an engine-driven fuel pump and an electrical boost pump. The fuel supply to each engine is controlled by an electrical shut-off valve. Both engines may receive fuel from either the forward or aft fuel tank by opening an electrically operated cross-feed valve. The aircraft is equipped with low fuel pressure and low fuel quantity caution annunciator lights, one for each engine. A low fuel quantity annunciator activates when 120 pounds, plus or minus 30 pounds, remain in their respective tank. The unusable fuel in the forward tank is 3.5 gallons and 6.0 gallons in the aft tank (a total of 63.7 pounds).

The operator reported that on January 26, 1993, the accident aircraft returned from an external load flight. Upon landing, the chief pilot who conducted the flight reported that the fuel gauges indicated 200 pounds of total fuel with 100 pounds each in the forward and aft tanks. No fuel was added following the flight. On January 27, 1993, the pilot of the accident aircraft flew .2 hours on an external load flight. There was no indication on the company fuel log that any fuel was added before or after that flight. On January 28, 1993, the pilot added 30 gallons (201 pounds) of fuel before the accident flight.

According to the operator, the helicopter normally operates with a basic fuel load of 200 pounds in each tank. The aircraft has an average fuel burn of 100 gallons (670 pounds) per hour.

National Transportation Safety Board investigators calculated the fuel on board at the time of the accident. Using an average weight of 6.7 pounds per gallon, and a fuel burn of 670 pounds per hour, the aircraft would consume 11.2 pounds per minute. The historical events and calculations indicate:

01/26/94 - aircraft landed with 200 pounds of fuel. 01/27/94 - pilot flew .2 hours, consuming 134.4 pounds of fuel. Fuel remaining would be 65.6 pounds.

01/28/94 - pilot added 201 pounds of fuel for a total of 266.6 pounds. An estimated 17 minutes of flight would consume 190.4 pounds of fuel for a total fuel remaining of 76.2 pounds.

The main rotor blades are constructed of 23, 11 1/2-inch by 10 1/2-inch-deep metal segments (pockets). These pockets are bonded to the blade spar and form the trailing edge of the blade.

Meteorological Information

The closest official weather observation station is San Jose, California, which is located about 1 1/2-nautical miles northwest of the accident site. At 0745 hours, a surface observation was reporting in part:

Sky condition and ceiling, clear; visibility, 35 miles; temperature, 37 degrees F; dew point, 32 degrees F; wind, calm; altimeter, 30.09 inHg.

Communications

Review of the air-ground radio communications tapes maintained by the FAA at the San Jose ATCT facility revealed that the aircraft successively and successfully communicated with the positions of ground and local control. No unusual communications were noted between the ATCT facility and the accident aircraft during the review of the tapes. A transcript of the air-to-ground communications between the aircraft and the ATCT facility is included in this report. The company crew working on the building was in radio communication with the pilot during the external load operation. A crew member reported that just prior to the engine sounds decreasing, he heard the pilot state on the company radio, "Oh, (expletive deleted)".

Wreckage and Impact Information

Safety Board investigators examined the helicopter wreckage at the accident site beginning on January 28, 1994, on the building roof at 675 N. 1st Street. The building roof area has three raised penthouse buildings that house various machinery. A vertical cement parapet about 14 feet high surrounds the entire building roof area along the building's outer edges. The central core penthouse is 34 feet long by 32 feet wide and has a two- level flat roof. The lower level is 15 feet wide and 14 feet high and houses a boiler and an air conditioning chiller. The upper level is 17 feet wide and 19 feet high and houses the elevator shaft and machinery. Several antennas were installed around the upper roof edge and were braced by wire strands. A large air conditioning cooling tower is located between the center and east penthouse. A sheet metal vent assembly on the upper roof area was crushed in a downward and westward direction. The vent housing displayed numerous parallel yellow/green paint transfer marks on the upper surface of the vent.

The penthouse upper level roof exhibited about an 18 inch oval- shaped depression located at the northwest corner of the upper level. The vertical cement edge of the upper roof was broken and scuffed adjacent to the roof depression. The helicopter's left main landing gear, strut, and landing light assembly separated from the fuselage and was located below the center penthouse roof, between the center and west penthouse. The helicopter rolled to the right and impacted the lower roof of the penthouse building, coming to rest on its right side. Scuff marks, black paint marks, and areas of broken concrete were noted on the south face of the building's north parapet wall.

Portions of the blades were located on the roof, on the ground to the east of the building, and in the parking lot to the west of the building. The external Kevlar cable was found draped from the air conditioning unit over the top of the center penthouse building and down to the wreckage. The main rotor transmission assembly with the rotor mast, blade roots, and supports, separated from the fuselage and was located upside down on the building roof next to the north edge of the center penthouse. The transmission assembly received fire damage as did the penthouse north wall and main building roof.

The lower penthouse roof, onto which the fuselage came to rest, was fire damaged. The helicopter's fuselage, from just aft of the engines to just forward of the tail wheel, was consumed by fire. The vertical tail of the fuselage with the tail rotor assembly attached, separated from the fuselage. It was positioned vertically along the north edge of the center penthouse wall with the tail rotor blades resting on the main building roof. The tail wheel was hooked on the top edge of the penthouse roof. The tail rotor blades remained attached to the gearbox and were not damaged. Drive shaft continuity from the point of separation forward of the intermediate gearbox to the tail rotor blades was established.

Due to the impact and postimpact fire damage, Safety Board investigators were unable to operate the flight controls by their respective control mechanisms. The collective assembly was found separated from the wreckage, lying over the north wall of the center penthouse. Examination of the left and right collective levers and dual throttle grips revealed that the throttle stop pins were positioned in the full open position. The collective mounted switches normally housed at the forward end of the collective levers were destroyed by fire on the pilot's collective (right side).

The postcrash fire incinerated the cabin and cockpit area. Safety Board investigators, however, recovered several extremely damaged instruments. The position of the instrument needles were compared to those of a sister aircraft. The main rotor transmission oil pressure gauge indicated 150 PSI. One needle of the dual hydraulic pressure gauge indicated about 500 PSI and a second needle indicated about 3,000 PSI. The dual needles on the engine torque gauge both indicated about zero. One fuel pressure gauge was recovered and the needle indicated about 15 PSI.

The main rotor yellow blade separated about 2 1/2 feet outboard from the root. It fragmented into two additional segments. A black, tar-like material was present on the leading edge at the tip and also on the leading edge at the midspan fracture point. The rotor hub exhibited denting adjacent to the spindle housing consistent with overtravel of the lead/lag hinge, primarily in a lag direction. The spindle was separated from the damper assembly.

The main rotor blue blade separated about 4 1/2 feet outboard from the root. It fragmented into three additional segments. The center section of the fragmented blade displayed 1 inch- to 1 1/2-inch-deep, leading-edge gouges that were spaced about 12 inches apart. The gouges exhibited braided wire-like impressions. The tip exhibited black tar-like material on the leading edge. The damper assembly remained attached to the spindle.

The main rotor red blade separated 2 feet outboard from the root. It fragmented into two additional segments. One segment was folded over about 180 degrees back onto itself. The blade tip displayed diagonal chordwise scratching from the leading edge to the trailing edge in an outboard direction. It also had tar-like material on the tip. The damper assembly remained attached to the spindle.

The main rotor black blade separated 2 feet outboard from the root. It fragmented into two additional segments. It also exhibited black tar-like material on the tip. The rotor hub exhibited denting adjacent to the spindle housing consistent with overtravel of the lead/lag hinge, primarily in a lag direction. The spindle was separated from the damper assembly.

There was no evidence of overtravel damage to the main rotor droop stops. All of the main rotor blades displayed leading-edge gouging, chordwise scratching, tip destruction, and upward curling. The fracture surfaces of all of the blades displayed multiple 45-degree-angle planes. The trailing edge of the blade segments exhibited buckling and compression.

Examination of the transmission revealed that the drive shaft from the angle gearbox was melted at the input pinon. All of the hydraulic, pitch change servos remained attached to their respective swash plate attach points. The servos remained attached to their respective bellcranks and the hydraulic reservoir was attached to the transmission. The transmission could not be rotated by hand during the initial inspection.

The engines sustained fire damage to the accessory gearcases. The inlets were unobstructed and the compressors both could be rotated by hand. Both engine's manual fuel control lever mechanical pointers were positioned at the 95 degree mark. Continuity between the engine power sections and the combining gearbox was established. Both engine power sections rotated by hand with an audible rubbing noise. The drive shaft from the combining gearbox to the angle gearbox was melted at the aft end of the engines. The angle gearbox sustained fire damage and impact damage to the lower front corner of the case.

The engine fire handles were recovered and examination revealed that one handle contained an undamaged light bulb that would illuminate if an engine fire was detected. The bulb filament was tightly coiled and undamaged.

Medical and Pathological Information

A postmortem examination of the pilot was conducted by the Santa Clara County Medical Examiner's Office, 850 Thornton Way, San Jose, California, on January 29, 1994. The examination revealed that the cause of death for the pilot was attributed to blunt chest trauma and thermal burns.

A toxicological examination was conducted by the Federal Aviation Administration Civil Aeromedical Institute (CAMI) on October 5, 1994. The examination was negative for all screened drugs and alcohol.

Fire Aspects

The aircraft fuselage above the lower floor is comprised of magnesium skin. Numerous structural components are also magnesium. After impact, the ground crew reported that a small postcrash fire erupted which quickly engulfed the aircraft. Hand fire extinguishers were unable to control the fire. Arriving fire department personnel employed hand lines connected to building water standpipes. Shortly after water was applied, the electrical supply to the building shorted out. This disabled the building elevator and required that subsequent fire department personnel, walk and carry equipment up the 13 floors to the roof.

Tests and Research

An examination of Sikorsky S58T fuel gauge accuracy and the low fuel level warning system was conducted on a sister aircraft utilized by another operator. The calibration was overseen by an FAA inspector from the San Jose, California FSDO. According to the manufacturer, the fuel gauges are calibrated for cruise flight which is about a 3-degree nose-down attitude. The fuel gauges would read slightly less when the aircraft is operated at a level hover. When the aircraft is parked, it rests in a nose- high attitude.

Additionally, the aircraft engines return excess fuel vapor during operation to the forward fuel tank only. The fuel return rate may vary from about 540 pounds per hour at high power settings, to 1,200 pounds per hour at flight idle. This may require the pilot to balance fuel by occasionally feeding both engines from the forward tank by means of the fuel crossfeed switch and isolation of the aft tank.

During the fuel calibration examination, engine deceleration times were recorded with the rotor blades at flat pitch (collective down). The engines decelerated from 93 percent Nf to flight idle in about 5 seconds. From flight idle to zero, when the engines were placed in idle cut-off, required 34 seconds.

On August 13, 1987, Safety Board investigators requested assistance from the FAA San Jose FSDO in overseeing several tests on the Sikorsky S58T fuel system configuration. These tests were conducted in conjunction with an accident investigation in Alaska. The pilot performing the tests was the pilot of this accident aircraft. The observations by the FSDO personnel indicted that both engines will continue to operate as long as there is fuel in the tanks, no matter if the boost pumps are on or off. Both engines will continue to operate with one tank empty as long as the boost pumps are on. Both engines will fail with one tank empty if there is no head pressure supplied to the engine driven fuel pumps from the tank with fuel. The FAA indicated that this could result from attempting to balance the fuel load by crossfeeding and turning off the pump to the low tank and letting the other tank run dry. Additionally, both engines will fail if fuel is being drawn from one tank, the other being empty, and experiencing a boost pump failure on the fuel tank containing fuel.

On February 11, 1994, Safety Board investigators conducted an examination of the main rotor transmission at California Helicopter International, Ventura, California. The main rotor input pinon module had been removed; however, the transmission remained frozen, unable to be turned by hand. The outboard end of the beveled pinon gear exhibited inward curling and circumferential distortion of the threads, outboard of the locking holes. During disassembly of the main rotor head, the mast began to move upon hand rotation. Continued disassembly did not reveal any malfunction of the transmission.

Beginning on May 3, 1994, Safety Board investigators conducted an engine examination at Pratt and Whitney Canada, Montreal, Canada. Refer to the Powerplant Group Chairman's Report contained in this report. The examination did not reveal any evidence to indicate whether either power section was rotating or not rotating at impact. The examination did not find any evidence of any preexisting failure or condition that would have prevented engine operation.

The aircraft warning annunciator panel received fire damage; however, it was removed and submitted to the Safety Board's Materials Laboratory for examination. No physical evidence concerning the status of the warning light bulbs prior to impact could be made.

Additional Information

FAA regulations specify that for operations conducted in VFR conditions, no person may begin a flight in a helicopter unless there is enough fuel to fly to the first point of intended landing, and assuming normal cruising speed, to fly after that for at least 20 minutes.

Rotorcraft external load operations are conducted under CFR 14 Part 133. The certificate holder or chief pilot must demonstrate his knowledge and skill in external load operations and have a letter of competency or logbook endorsement from an FAA inspector. A demonstration of proficiency need not be shown if the inspector finds that the chief pilot's previous experience is adequate. Other company pilots must demonstrate their external load knowledge and skill to the FAA or the chief pilot and be similarly endorsed. Annual recurrent training is not required if a pilot has performed external load operations within the previous 12 months.

The operating rules allow for operations closer than 500 feet to the surface, persons, vessels, vehicles, and structures, and over congested areas, if they are conducted without creating a hazard to persons or property on the surface. Additionally, the operator must develop a plan for each external load operation that is approved by the FAA. The plan must include an agreement with local authorities for the exclusion of unauthorized persons from the area of operations, coordination with air traffic control if necessary, and a chart depicting flight routes and altitudes. The flight must be conducted at an altitude and route that will allow a jettisonable external load to be released, and the helicopter landed, in an emergency without hazard to persons or property on the surface.

The operator prepared an external load plan for the accident flight operation that was approved by the San Jose FSDO on January 27, 1994, with a note that the operation was to be monitored by an FAA inspector. The operator had conducted two previous external load operations at the accident site building (total of three). The pilot conducted the most recent flight to the location on January 6, 1994, and logged .2 hours of flight time for the operation.

The load plan included building site information that stated the top two floors of the building would be evacuated and if the load were jettisoned, one floor of the building could possibly be penetrated. The operator submitted a diagram of the area of operation that depicted the placement of security personnel, barricades, the building roof, and a landing zone in the west parking lot. The diagram included a notation of 20-foot-high trees in the parking lot and homes and a school located south of the building. An examination of the diagram by Safety Board investigators revealed that it oriented the building, the placement of the rooftop penthouse buildings, and the parking lot, 90 degrees from the physical location of the building. In addition, the diagram noted only two penthouse buildings instead of three.

The FAA's inspectors handbook defines an operational area as being devoid of members of the nonparticipating public. An emergency landing site requires that the aircraft be at an altitude that will allow landing in an emergency without hazards to persons or property on the surface. There is no requirement that the emergency landing be made without damage to the helicopter. An emergency landing site does not have to be an improved surface. The landing site should be of such quality that the pilot, in considering his or her personal survival, could be reasonably expected to use it.

The FAA inspector who approved the load plan is the principle operations inspector (POI) for the company. He reported that the load plan was approved by a desk review of the information provided by the operator. That information included two previous lift operations at the accident building and a hand-drawn sketch of the area. The inspector did not personally review the plan with the pilot or visit the lift site; however, he was familiar with the pilot's skills and arranged for another inspector to monitor the lift. The inspector indicated that based on the lift plan's diagram, the emergency landing area would have been the building roof.

Wreckage Release

The Safety Board released the helicopter wreckage, located at Reid Hillview Airport, San Jose, California, to the owner's representative on February 17, 1994. The engines and the annunciator panel were retained by the Safety Board for examination until their release on May 16, 1994.