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NTSB releases Cirus SR20 crash informationNTSB releases Cirus SR20 crash information

NTSB releases Cirus SR20 crash information

The National Transportation Safety Board (NTSB) has released an advisory on what has been learned so far in the investigation of the March 23 accident involving an experimental Cirrus SR20 that crashed near the Duluth International Airport.

The NTSB led the investigation team, which included personnel from Cirrus Design and the FAA. “Cirrus applauds both the NTSB and the FAA for their cooperation and expediency in the investigation,” said Alan Klapmeier, president of Cirrus Design. The company has completed extensive retesting and analysis of the control system, both of which exceed FAA requirements and substantiate the safety of the design.

From what Cirrus has learned in the investigation and to ensure this type of control interference cannot occur again, the following changes have been made to the SR20:

  • Aileron leading edges have been closed, eliminating potential interference with wing trailing edge.
  • Clearance between aileron and wing trailing edge has been expanded.
  • Elevator leading edges have been closed, eliminating potential interference with horizontal trailing edge.
  • Clearance between elevator and horizontal trailing edge has been expanded.
  • Wing aileron coves were attached differently to prevent the possibility of aileron leading edge interference.
  • Aileron actuation pulley control stops have been modified.

Testing of the above modifications has been an important part of the company’s flight test schedule for the past six weeks. Those tests were conducted on two SR20 aircraft. Cirrus is confident that the above changes address all issues associated with the accident and clear the way for delivering SR20s to customers.

Delivery of the first customer aircraft, which made its first flight June 7, awaits FAA issuance of an airworthiness certificate. Prior to that, Cirrus will have to implement the above modifications, and the FAA will have to complete the required documentation associated with those modifications.

The NTSB has issued a press release based on early evidence. It can be found on the Web. Here are two excerpts from that press release:

“The airplane made several right turns as it climbed to a maximum altitude of 6,500 feet above mean sea level. The airplane then began a descent and a turn to the left about the time that the pilot declared an emergency. Radar data and ground eyewitness statements indicate that the airplane made only turns to the left as it approached the airport. About 2 miles north of the airport, the pilot reported a flight control problem. The airplane subsequently impacted terrain in a nose-down, left-wing low attitude south of the airport after two passes along Runway 27. Gusting winds from the northwest prevailed at the time.”

“Examination of the wreckage revealed no evidence of a fire or in-flight structural failure. Also, no pre-impact failures or malfunctions with the engine, propeller, or systems were found, except for the flight control system of the roll axis. Examination of the wing and aileron structure revealed scratch and rub marks on the upper surface of the right wing skin near the mating area of the right aileron. Corresponding marks were found on the leading edge of the right aileron. Static testing on other Cirrus SR20 prototypes revealed that it is possible for the leading edge of the right aileron to become jammed against the wing when the aileron is deflected downward and the wing is flexed upward to its maximum design limit. The gap tolerances between the aileron and wing are critical factors in determining the potential for jamming.”

June 20, 1999

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