Conflicting information on airport traffic procedures and private-company operating rules appear to be among the factors the NTSB is reviewing in assessing the cause of a fatal 2014 midair collision between a flight school Robinson Helicopter R44 II and an airplane, according to safety board records released April 23.
The collision occurred about 1 mi southwest of Frederick Municipal Airport (FDK) in Frederick, Maryland, at 3:37 p.m. local time on Oct. 23, 2014, as a privately operated Cirrus Aircraft SR22 was turning onto a left downwind approach to Runway 30 and as the R44 from Advanced Helicopter Concepts was beginning an instructional flight. Visual meteorological conditions prevailed.
The helicopter flight instructor, student and a passenger died of blunt-trauma injuries suffered in the R44 crash. The Cirrus pilot deployed that aircraft's parachute after the midair; he and his passenger survived, the passenger with minor injuries.
The presidential appointees on the NTSB now must review investigators' findings and recommendations to determine a probable cause of the accident.
Data gathered by the NTSB indicates that the collision occurred below FDK's published traffic pattern altitude of 1,300 ft msl for small fixed-wing airplanes. Information recovered from the solid-state air data and attitude heading reference system in the Cirrus' Avidyne primary flight display indicated the airplane "experienced a loading event" in pitch, vertical, longitudinal and lateral acceleration at 3:37:36 p.m., the NTSB said.
At that point, the recovered data shows, the Cirrus was at a pressure altitude of 1,045 ft. A split second earlier, the NTSB said, the air traffic controller had directed the R44 pilot to "stay at 1,000 ft. I have traffic in the downwind."
The NTSB noted that the R44 never appeared on radar at the Potomac Terminal Radar Approach Control (TRACON) that covers the FDK area. “At the time of the accident, the floor of the Potomac TRACON radar coverage in the area surrounding FDK appeared to be about 1,200 feet mil," the safety board said.
Investigators said they found conflicts among information from control tower personnel, the helicopter operator, the airport operator and FAA
guidance about the traffic pattern altitude used for helicopters operating at FDK, according to a report and supporting documents that the NTSB released April 23.
In seeking to establish traffic pattern data for FDK, the NTSB said, investigators learned from the air traffic manager at FDK’s contract-operated control tower said that no helicopter pattern altitude had been published in the FAA
's Airport/Facility Directory at the time of the collision.
That manager, the controller handling the accident aircraft and an off-duty controller who witnessed the collision all told the NTSB that the pattern altitude for helicopters was 900 ft msl. They said those for small fixed-wing airplanes and for large fixed-wing and for twin-engine ones were 1,300 ft msl and 1,800 ft msl, respectively, the safety board said. It added that the fixed-wing altitudes had been published in the facility directory.
Before the crash, the NTSB said, the city of Frederick (which owns the airport) had published and distributed a pamphlet and posters that showed airport traffic patterns and identified the helicopter pattern altitude as 1,100 ft msl.
The NTSB noted that the FAA's Aeronautical Information Manual states that, in the absence of a published pattern altitude for helicopters, that altitude is 500 ft agl, or about 800 ft msl at FDK.
The FDK air traffic manager said the 900 ft helicopter pattern altitude "was agreed upon during meetings with tower personnel, airport management, and airport tenants prior to the tower's commissioning" in 2012, according to the NTSB, but "the facility was unable to produce any documentation that these meetings were ever held" or that a 900-ft had been set. The safety board said the FAA requires minutes of such meetings to be recorded and distributed.
An owner/operator of Advanced Helicopter Concepts told investigators that the flight school had no standard operating procedures "and no published procedures," according to the NTSB. He said the helicopter pattern altitude had "just kind of morphed into" 900 ft msl, which he had chosen, it added, quoting him as saying, "The airplanes are at 1,300 feet and we thought we should be below that."
Photo courtesy of NASA