Urban Air Sro UFM-13 N17UA

Summary

On 23 June 2009 at about 17:49 local time, a Urban Air Sro UFM-13 registered N17UA, operated by San Antonio Light Sport Aircraft, Inc., was involved in an accident near Bourne Stage, Texas, United States. One person was on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

23 June 2009 at 17:49

Classification

Accident

Location

Bourne Stage, Texas, United States

Coordinates

29.5336, -98.4697

Aircraft

Urban Air Sro UFM-13

Registration

N17UA

Category

Glider

Engines

1

Operator

San Antonio Light Sport Aircraft, Inc.

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Boerne Stage → Boerne Stage

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN09LA379

Nobody was injured.

The pilot’s exceedance of the aircraft’s placarded never-exceed speed (Vne), resulting in aerodynamic flutter in the empennage and the subsequent in-flight structural failure of the aft portion of the fuselage.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The pilot noticed a light fluttering of the rudder pedals that stopped when he applied gentle foot pressure. The motor glider was in level cruise flight when it suddenly began to shake violently, throwing the pilot back and forth against his restraints. He said that the airspeed was about 80 KIAS (knots indicated airspeed); however, data available from the airplane’s on-board Global Positioning System (GPS) indicates that the aircraft was flying approximately 110 KCAS (knots calibrated airspeed). The pilot deployed the emergency ballistic parachute and the aircraft landed gently on top of small trees, sustaining additional damage. Postaccident examination of the motor glider revealed the empennage had separated from the fuselage, but remained attached by control cables and tubing. GPS data showed the aircraft’s airspeed had gradually increased to about 110 KCAS when the in-flight breakup occurred. After a similar accident in the Czech Republic, the never-exceed speed (Vne or redline) was lowered from 119 KCAS to 81 KCAS. The accident airplane’s airspeed indicator had two redlines: one was at 119 knots and the other was taped onto the instrument glass at 81 knots and was in the middle of the green arc. The pilot said that he was not aware that the Vne speed was 81 KCAS, but that the change was a temporary flight recommendation from the manufacturer. He said that he had received the memorandum containing the temporary restriction on airspeed not to exceed 81 KCAS in any configuration, but that he “did not think the 81 knots was a Vne speed.” The manufacturer had lowered the Vne as a temporary measure because of a previous accident where an in-flight structural failure of the aft portion of the fuselage occurred. The investigation of the first accident by Air Accident Investigations Institute, Republic of Czechoslovakia, determined that the separation was the result of aerodynamic flutter in the empennage. According to the NTSB’s Materials Laboratory report, the fractures were consistent with compressive loads and tension or tearing from local bending. No evidence of manufacturing errors or preaccident damage was noted.

Quoted verbatim from the NTSB record.