# NTSB FTW04LA148: Bruce Moore Skybolt, N25BM, Altus, OK, May 23, 2004 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: May 23, 2004, 13:00 local (18:00 UTC) - Place: Altus, OK - Coordinates: 34.698612, -99.338058 - Nearby events: https://openairdocs.org/map.md?lat=34.6986&lon=-99.3381&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report September 29, 2004 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 59372 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW04LA148 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/59372/pdf - Page: https://openairdocs.org/ntsb/FTW04LA148 ## Probable cause The partial in-flight separation of the wing fabric and rib structure due to an inadequate material installed by the airplane builder. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - wing,skin - separation (cause) - wing,wing rib - separation (cause) - material inadequate, owner/builder (cause) - Forced landing, descent - emergency ## Analysis The pilot was performing aerobatic maneuvers when he noticed the fabric on the top right wing was separating and departing the airplane. The pilot reduced the engine power, airspeed, and altitude, and then returned to the airport. Examination of the airplane revealed the wing rib stitching had failed, and approximately 5 feet of the top right wing fabric and approximately 3 feet of the top right wing lower fabric was separated. According to a fabric manufacturer technical bulletin, "When light weight fabric is installed on an aircraft with a high horsepower engine and inadequate fabric forming structural spacing, coating fatigue cracks develop very rapidly...We recommend fabric weighing less than 2.4 [ounces] per [square yard] be used only on aircraft with engines up to 145 [horsepower]." The fabric covering weight on the airplane was 1.7 ounces per square yard, and the airplane was equipped with a 300-horsepower engine. ## Factual narrative On May 23, 2004, approximately 1300 central daylight time, a Bruce Moore Skybolt homebuilt single-engine aerobatic bi-plane, N25BM, sustained substantial damage following a partial in-flight breakup while maneuvering near Altus, Oklahoma. The commercial pilot, who was the registered owner, and a passenger were not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight departed the Altus/Quartz Mountain Regional Airport (AXS), Altus, Oklahoma, at an unknown time. According to the Federal Aviation Administration inspector, who responded to the accident site, the pilot was performing aerobatic maneuvers when he noticed the fabric of the top right wing was separating and departing the airplane. The pilot reduced the engine power, airspeed, and altitude, and then returned to AXS. Examination of the airplane revealed the wing rib stitching had failed, and approximately 5 feet of the top right wing fabric and approximately 3 feet of the top right wing lower fabric was separated. One wing rib was damaged and two trailing edge ribs were separated. The fabric covering weight was 1.7 ounces per square yard. The airplane was equipped with a 300-horsepower Lycoming IO-540 engine. At the time of the accident, the airframe had accumulated approximately 116 total flight hours. The date and time since the last inspection was unknown. According to Poly Fiber Aircraft Coatings Technical Bulletin 89-1D, dated October 1989, Aircraft Fabric Drumming, "When light weight fabric is installed on an aircraft with a high horsepower engine and inadequate fabric forming structural spacing, coating fatigue cracks develop very rapidly...We recommend fabric weighing less than 2.4 [ounces] per [square yard] be used only on aircraft with engines up to 145 [horsepower]...Sometimes fabric is pressed or beat against close underlay structure which causes a crowfoot break in the coatings after 50 to 100 [hours]." Numerous attempts to obtain a completed Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) from the pilot were unsuccessful. ## Aircraft - Registration: N25BM (not matched to a registry record) - Reported make and model: Bruce Moore Skybolt - Category: Airplane, amateur-built - Serial number: S-BM-001 - Engines: Lycoming IO-540-D4A5 300 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Clark A. Murray - Airworthiness certificate: Special, Experimental (Special) - Departed: AXS, Altus, OK - Airport: AXS, Altus Municipal ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 60; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; last flight review September 15, 2003; flight hours: 30 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 200° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 93 °F, dew point 36 °F - Altimeter: 29.72 inHg - Observed at: HBR, 22 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20040523015629A](https://openairdocs.org/incident/20040523015629A), May 23, 2004: Amtr SKYBOLT, Altus, OK, Substantial damage. (-23) During aerobatics maneuvers the pilot noticed the fabric of the top wing right side coming loose and departing the aircraft. The pilot reduced power,… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.