N904PD

1.1 HISTORY OF FLIGHT

On October 25, 1999, at 1537 hours Pacific daylight time, a MD Helicopter, Inc. (MDHI) 500N helicopter, N904PD, collided with a city street in San Jose, California, following an in-flight loss of control during an approach to the San Jose International Airport. The helicopter, operated by the City of San Jose Police Department as a public-use flight under the provisions of 14 CFR Part 91 of the Federal Aviation Regulations, was destroyed during the collision sequence. The airline transport pilot and nonrated passenger were fatally injured. Visual meteorological conditions prevailed and a company flight plan was filed. The flight originated about 1524 from Reid-Hillview airport and was en route to San Jose International Airport.

While on a routine patrol on October 23, 1999, the pilot and a police observer, who was flying the aircraft, experienced an uncommanded yaw of about 10 degrees to the right while practicing stuck pedal maneuvers. In his statement, the observer reported that after ascertaining that neither of them had made a control input, the pilot took control and made a precautionary landing at the Reid-Hillview airport. The observer said that the pilot reported the pedals felt mushy, but he had control authority. The next day a contract maintenance technician arrived and was unable to find a discrepancy in the anti-torque control system (see Aircraft Information for a more detailed discussion). The pilot and technician believed the problem was in the Yaw Stability Augmentation System (YSAS), and it was deactivated in accordance with the Rotorcraft Flight Manual (RFM) procedures in order to fly the helicopter back to the maintenance base at San Jose International. Prior to departing on the accident flight, the pilot made several left and right pedal turns while in a hover.

A review of the air-ground communications tapes from the San Jose International Air Traffic Control Tower (ATCT), revealed that the pilot contacted the facility about 4 miles east of the airport and requested landing at taxiway "Victor." The pilot was cleared to crossover the airport midfield at or above 1,000 feet agl for a left downwind. He was given the wind, altimeter setting, and transponder code. The pilot read back the instructions. Runways 30R, 30L, and 29 were in use. The pilot stated he was going to Aris Helicopters and was cleared to land on taxiway "Victor" paralleling the active runways. His next transmission at 1535:21 was "Police 1, mayday, mayday," and then again "mayday, mayday" 3 seconds later. Witnesses reported seeing the helicopter yawing erratically then descending rapidly while spiraling.

Controllers on duty in the ATCT observed the helicopter while on downwind for runway 29. One controller observed the helicopter "in erratic flight . . . (then) . . . plummet to the ground." Another controller observed the helicopter "approximately 1 to 1 1/4 mile base leg when it just fell out of the sky." Another controller assumed that the pilot was performing an autorotation and queried the others about the maneuver. The last controller observed the helicopter in a tight spiral on the left downwind and alerted the supervisor.

Twenty-one ground witnesses were identified and interviewed. Of the 21 witnesses, 15 observed the helicopter spin, although only 4 were able to quantify the direction as a "counter clockwise" rotation. Eight of the witnesses said they heard unusual engine sounds and they variously described them as "whining" or "choking/sputtering." One of the witnesses reported a "tighter and tighter" spin as the helicopter descended, while another said it was a "tight 180-degree turn." One witness said the tail "appeared to be bouncing back and fourth," while a second witness observed that the helicopter "started to rotate [one direction] and reversed direction," then spiraled straight down.

1.1.1 Radar Derived Flight Path

Recorded radar data in the form of a CDR Editor listing was obtained from the San Francisco Bay Terminal Radar Approach Control (TRACON). The data was recorded and processed by the TRACON's ARTS IIIA system using a surveillance antenna at the Moffett Federal Airport, located about 8 miles northwest of the accident site. The antenna rotates clockwise at a 4.7-second sweep rate. The data reviewed was the time of each secondary beacon return, the recorded target position, the Mode C altitude, ground track heading, and ground track speed. According to the facility, the ARTS IIIA system computes target ground speed and ground track heading based on a smoothing algorithm, which averages the last several data points.

In addition, recorded plot data was obtained from the San Jose International Airport noise abatement monitoring office. The facility obtains a direct feed of radar data from the Bay TRACON ARTS IIIA system and incorporates sound microphone decibel data to form an integrated picture of the tracks of departing, arriving, or over flight aircraft at the airport. The raw recorded radar data is processed in a computer program, Airport Noise and Operations Monitoring System (ANOMS), written by Lochard Company. The ANOMS program also uses a smoothing algorithm to compute and present target ground speed and track heading information.

Recorded raw radar data (time, position, and Mode C altitude) was also processed in a computer program Tactical Mapping by ERM, Inc. This program computes target point-to-point airspeed and heading without smoothing algorithms.

The tabular and graphically plotted radar data from all three sources is appended to this report.

Review of the data disclosed that the secondary beacon return was tracking west on a heading averaging 270 degrees at a Mode C reported altitude of 1,100 feet and a ground speed, which varied from 104 knots to 119 knots. As the target track passed over the airport midfield, the ground track heading turned left over the time frame 1534:16 to 1535:12 from 268 degrees to 126 degrees. The computed rate of turn was 2.4 degrees per second. Over the same time interval, the ground speed decreased to 115 knots. According to the air-ground communications tapes, 11 seconds after achieving the 126-degree heading, the pilot broadcasted the first "mayday" call. During this 11-second time interval, the Mode C reported altitude decreased to 900 feet as the ground speed decreased to 103 knots. Coincident with the "mayday" call, the Mode C reported altitude jumped from 900 to 1,100 feet in one 4.7-second radar antenna sweep interval, followed in the next 4.7-second sweep with a decrease to 800 feet. Over this same 9.4-second time frame, the ground speed decreased to 80 knots. The last secondary beacon return was recorded at 1535:31. Point-to-point computation of the ground track speed over the last four 4.7-second antenna sweeps yielded speeds of 79.7, 72.8, 56.3 and 23.2, then ground impact.

1.5 PERSONNEL INFORMATION

Review of the Federal Aviation Administration (FAA) Airman Certification records disclosed that the pilot held an airline transport pilot certificate with a multiengine land airplane rating. In addition, he held commercial pilot privileges for single engine airplanes land and sea, and rotorcraft-helicopter. The pilot held an instrument rating for airplanes and helicopters. He also held a flight instructor certificate with ratings for single and multiengine airplanes, rotorcraft-helicopter, and instruments. The most recent second-class medical certificate was issued to the pilot on October 30, 1998, and contained no limitations.

According to San Jose Police Department (SJPD) records, the pilot had accumulated a total flight time of 2,586 hours, consisting of about 1,215 hours of military helicopter flight time, and about 1,266 hours in the MDHI NOTAR (No Tail Rotor) helicopter. In the preceding 90 and 30 days, the pilot had flown 88 and 31 hours, respectively, in the 500N helicopter.

1.5.1 Pilot Training

The records indicate that the pilot successfully completed a MDHI 500N NOTAR Pilot's Recurrent Flight Training Course conducted at the Mesa, Arizona, factory on May 11, 1999. The course included both ground and flight instruction in anti-torque failure emergency procedures in the helicopter. The pilot's SJPD training file is attached to this report.

The pilot was also a member of the California Air National Guard (CANG) assigned to the 129th Rescue Wing based at Moffett Federal Air Field, San Jose. He is a designated military aviator assigned to fly the HH-60G helicopter as first pilot. The HH-60 is the Air Force version of the Army UH-60, commonly known as the Blackhawk. According to the pilot's military records, he transitioned to the HH-60 helicopter during an active duty training period from April through September 1996. As of his last flight with the CANG on October 22, 1999, the pilot had accumulated a total flight time in the HH-60 of 416 hours, with 120 hours flown in the past 12 months. According to the wing safety officer, during the pilot's initial transition training in 1996, he would have been given a very thorough indoctrination in the emergency procedures specific to the HH-60, including the loss of anti-torque capability. In addition to the initial transition training, the wing safety officer reported that pilot had routine refresher training during the year with various unit instructor pilots. His most recent recurrent emergency procedures training in the HH-60G with the unit was on October 15, 1999.

Review of the anti-torque failure procedures for the MDHI 520N and the HH-60G revealed that they are diametrically opposed to one another. A detailed discussion of the two procedures can be found under AIRCRAFT INFORMATION, paragraph 1.6.3. Additional information on this topic can be found in TESTS AND RESEARCH, paragraph 1.16.6.

1.5.2 Maintenance Technician Certification and Training

The maintenance technician who examined the helicopter ...