# NTSB CEN09LA379: Urban Air Sro UFM-13, N17UA, Bourne Stage, TX, June 23, 2009 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 23, 2009, 12:49 local (17:49 UTC) - Place: Bourne Stage, TX - Coordinates: 29.533611, -98.469718 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.5336&lon=-98.4697&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report March 16, 2011 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA Flight Standards - NTSB case key (mKey): 74117 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN09LA379 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/74117/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=74117 - Page: https://openairdocs.org/ntsb/CEN09LA379 ## Probable cause 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. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Performance/control parameters: airspeed](https://openairdocs.org/ntsb-findings/01062010): Aircraft › Aircraft oper/perf/capability · Capability exceeded (probable cause); cases with it: [Urban Air Sro UFM-13 LAMBADA, 1 case](https://openairdocs.org/ntsb-findings/01062010/cases.md?model=060003D), [All aircraft, 1,681 cases](https://openairdocs.org/ntsb-findings/01062010/cases.md) - [Fuselage: fuselage main structure](https://openairdocs.org/ntsb-findings/01035310): Aircraft › Aircraft structures · Failure (probable cause); cases with it: [Urban Air Sro UFM-13 LAMBADA, 1 case](https://openairdocs.org/ntsb-findings/01035310/cases.md?model=060003D), [All aircraft, 24 cases](https://openairdocs.org/ntsb-findings/01035310/cases.md) - [Action: incorrect action performance](https://openairdocs.org/ntsb-findings/02041015): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Urban Air Sro UFM-13 LAMBADA, 1 case](https://openairdocs.org/ntsb-findings/02041015/cases.md?model=060003D), [All aircraft, 1,386 cases](https://openairdocs.org/ntsb-findings/02041015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) (defining event); cases with it: [Urban Air Sro UFM-13 LAMBADA, 1 case](https://openairdocs.org/ntsb-events/337/sequence.md?model=060003D), [All aircraft, 290 cases](https://openairdocs.org/ntsb-events/337/sequence.md) ## Analysis 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. ## Factual narrative On June 23, 2009, at 1249 central daylight time, an Urban Air SRO UFM-13 Lambada, N17UA, registered to and operated by San Antonio Light Sport Aircraft, Inc., was substantially damaged when the fuselage failed in-flight over Boerne Stage, Texas. Visual meteorological conditions prevailed at the time of accident. The personal flight was conducted under provisions of 14 Code of Federal Regulations (CFR) Part 91 without a flight plan. The private pilot was not injured. The local flight originated at Boerne Stage Field (5C1), at 1202. According to the pilot, this was his first flight in the motor glider. During the early portion of the flight, he noticed a "light fluttering of the rudder pedals" that stopped when he applied "gentle" foot pressure. At the time of the breakup, the aircraft was in level cruise flight at 3,500 feet when it suddenly began to “shake violently.” The pilot was thrown back and forth in the cockpit against his restraints. The pilot said that the airspeed was about 80 KIAS (knots indicated airspeed). However, available data indicates that the aircraft was flying approximately 110 KCAS (knots calibrated airspeed). He immediately reduced power and the nose of the motor glider pitched down to a near-vertical attitude. He deployed the emergency ballistic parachute, and the aircraft landed "gently" on top of small trees, sustaining additional damage. The pilot said that from the time the shaking began until deployment of the parachute, 2 to 2-1/2 seconds had elapsed. Examination of the motor glider revealed the empennage had separated from the fuselage, but remained attached by control cables and tubing. Another pilot who had flown this same motor glider on a previous flight said he had also experienced “rudder flutter.” The pilot later examined the tail structure of the aircraft and said it appeared that there were no structural supports in the tail, that “it is just a hollow fiberglass tube.” He attributed the lack of structural components to the requirement for light sport aircraft to be below a specific weight in order to qualify for the “light sport” category. A GPS (Global Positioning System) was installed in the airplane for navigation. It recorded time, position, altitude, ground speed and ground track at one-second intervals. A National Transportation Safety Board (NTSB) performance engineer used this data along with temperature and wind data to determine the flight parameters for the Lambada Motor Glider. The data show that the climb was normal at about 1000 fpm, gradually slowing to 500 fpm. Airspeed varied between 60 and 80 KCAS. The airplane leveled off at 6,000 feet and briefly accelerated to about 90 KCAS. For the next 15 minutes, the airplane traveled in an outbound direction at about 6,000 feet and 80 KCAS. The maneuvers appeared gentle. The airplane made several turns over the San Antonio area and then turned to an inbound course to Borne Stage Field (northeast of San Antonio, TX). It accelerated to about 100 KCASand descended to 5,000 feet. The airplane flew relatively straight at 5,000 feet and 100 KCAS for about 7-1/2 minutes. At that point, the airplane appeared to start a descent and the airspeed had gradually increased to about 110 KCAS. That is when the in-flight breakup occurred. The failed portion of the fuselage was sent to NTSB’s Materials Laboratory for examination. The following are excerpts from the report: “In the area of the fracture, the fuselage was nearly circular. The fractures were oriented nearly perpendicular to the fuselage axis, and the fracture surfaces had a flattened or crushed appearance consistent with fracture under primarily compressive loads. In addition, the composite material showed evidence of in-plane delaminations adjacent to the fractures, consistent with fracture under primarily compressive loads. The fractures were generally at more of an angle to the fuselage axis, and the fracture surfaces had a more fibrous appearance, consistent with fracture under tension or tearing from local bending. The disbond fracture along the seam revealed the surfaces of the glass fabric making up the composite, indicating that fracture occurred in the matrix material adjacent to the fabric rather than in the adhesive. Although the fracture through the fuselage ran across the lap joint seam at the top of the fuselage, that seam showed no evidence of any significant disbonding. There was no evidence of any manufacturing errors or pre-existing damage such as fatigue cracking.” After a similar accident in the Czech Republic, the never-exceed speed (Vne or redline) was lowered from 119 KCAS to 81 KCAS. N17UA’s airspeed indicator had two redlines displayed. 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 he had received the memorandum containing the “temporary restriction on airspeed not to exceed 81 knots in any configuration,” but he “did not think the 81 knots was a Vne speed,” and noted that at ¾ throttle, the motor glider was “way past 81 knots.” He believed the change was a “temporary flight recommendation” from the manufacturer pending completion of another accident investigation involving an in-flight break-up that occurred in Czechoslovakia. In that accident, the aft portion of the fuselage structure failed in-flight as the result of aerodynamic flutter in the empennage. The accident report was issued by the Air Accident Investigations Institute, Republic of Czechoslovakia (Ref. No. CZ-09-046, FINAL REPORT, Investigation of Microlight Aircraft Accident, Type UFM 13 Lambada, Registration Mark OK-NUA 09, on 21st March 2009). According to this report, “the most likely cause of the accident was “flutter”, an aeroelasticity phenomenon, which occurred on the horizontal tail surface bringing about a loss of integrity of the fuselage and in-flight separation of its rear part.” As a result of the investigation, the manufacturer of the UFM-13, UrbanAir, issued Mandatory Service Bulletin UFM-13-1/2009, dated March 24, 2009, that required the inspection and reinforcement, if necessary, of the elevator hinges in the horizontal stabilizer. The bulletin also required that Vne be decreased to 81 KCAS. Seven months prior, on August 17, 2009, the company had issued Mandatory Service Bulletin UFM-13-2/2009, following reports of damaged elevator hinges as a result of the inspection program, and provided instructions for reinforcing the hinges. Because of these bulletins, the horizontal stabilizer and elevator were also sent to NTSB’s Materials Laboratory for examination. According to that report, “The Urban Air service bulletins require a visual inspection of the Y-shaped hinge fittings on the horizontal stabilizer for damage or delamination or inordinate deflection while applying upward and downward forces of 1 to 2 pounds (5 to 10 Newtons) at the position of the hinge pin. Carrying out the procedure in the service bulletins revealed no damage or excessive deflection of any of the five hinge fittings on the horizontal stabilizer. The five hinge pins on the elevator itself were also inspected, and no damage was found at any of the hinge pins.” ## Aircraft - Registration: [N17UA](https://openairdocs.org/deregistered/N17UA-2013-04-22), registration cancelled 2013-04-22, S/N 113/13 (OpenAirDocs) - Reported make and model: Urban Air SRO UFM-13 (Lambada) - Registry model: [Urban Air Sro UFM-13 LAMBADA](https://openairdocs.org/model/urban-air-sro-ufm-13-lambada) (registry code 060003D) (OpenAirDocs) - Registry engine: [Rotax 912ULS series](https://openairdocs.org/engine/rotax-912uls-series) (registry code 55572, 4 cycle) (OpenAirDocs) - Category: Glider - Serial number: 113/13 - Engines: Rotax 912ULS 100 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: San Antonio Light Sport Aircraft, Inc. - Registered owner: San Antonio Light Sport Aircraft, Inc. - Airworthiness certificate: Special, Experimental light sport (Special) - Departed: 5C1, Boerne Stage, TX - Destination: 5C1, Boerne Stage, TX ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: with waivers/limitations; seat: left; flight hours: 633 total, 11 in this make and model, 559 as pilot in command, 10 in the last 90 days, 9 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 140° at 5 knots - Visibility: 10 statute miles - Temperature: 91 °F, dew point 64 °F - Altimeter: 29.92 inHg - Observed at: SAT, 13 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 20090623017659A](https://openairdocs.org/incident/20090623017659A), Jun 23, 2009: Urbana UFM13LAMBADA, Boerne, TX, Substantial damage. (-23) Pilot was at cruse at 3000 ft AGL. Aircraft started an extreme violent vibration. Lasting approximatey 2 to 3 seconds, then had a hard nose down… ## Docket (18 files) The files NTSB released with the investigation on December 14, 2010, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=74117. 21.8 MB in all. - NTSB Form 6120.1-2, Pilot-Operator Aircraft Accident Report (item 1, .PDF, 10.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338246&FileExtension=.PDF&FileName=NTSB%20Form%206120.1-2,%20Pilot-Operator%20Aircraft%20Accident%20Report-Redacted.PDF - Materials Laboratory Factual Report 10-083, Fuselage fracture and empennage (item 2, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40335882&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2010-083,%20Fuselage%20fracture%20and%20empennage-Master.PDF - Materials Laboratory Factual Report 10-088, Empennage and elevator hinges (item 3, .PDF, 827 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336391&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2010-088,%20Empennage%20and%20elevator%20hinges-Master.PDF - Lambada Performance Study (item 4, .PDF, 13 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338520&FileExtension=.PDF&FileName=Lambada%20Performance%20Study-Master.PDF - Last Flight Data (item 5, .PDF, 80 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338463&FileExtension=.PDF&FileName=Last%20Flight%20Data-Master.PDF - GPS Plots (item 6, .PDF, 562 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338550&FileExtension=.PDF&FileName=GPS%20Plots-Master.PDF - Graphs from GPS (item 7, .PDF, 6.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338503&FileExtension=.PDF&FileName=Graphs%20from%20GPS-Master.PDF - ZB UFM-13 Mandatory Bulletin (item 8, .PDF, 111 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338471&FileExtension=.PDF&FileName=ZB%20UFM-13%20Mandatory%20Bulletin-Master.PDF - Weather Reports and Records (item 9, .PDF, 164 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338588&FileExtension=.PDF&FileName=Weather%20Reports%20and%20Records-Master.PDF - Photo 1. N17UA at the accident site. (item 10, .PDF, 378 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338509&FileExtension=.PDF&FileName=Photo%201.%20N17UA%20at%20the%20accident%20site.-Master.PDF - Photo 2. N17UA after recovery to a salvage yard. (item 11, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338512&FileExtension=.PDF&FileName=Photo%202.%20N17UA%20after%20recovery%20to%20a%20salvage%20yard.-Master.PDF - Photo 3. Failed fuselage. (item 12, .PDF, 50 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338511&FileExtension=.PDF&FileName=Photo%203.%20Failed%20fuselage.-Master.PDF - Photo 4. Failed fuselage. (item 13, .PDF, 29 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338513&FileExtension=.PDF&FileName=Photo%204.%20Failed%20fuselage.-Master.PDF - Photo 5. Failed fuselage. (item 14, .PDF, 38 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338514&FileExtension=.PDF&FileName=Photo%205.%20Failed%20fuselage.-Master.PDF - Photo 6. N17UA's Airspeed Indicator. (item 15, .PDF, 31 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338521&FileExtension=.PDF&FileName=Photo%206.%20N17UA%27s%20Airspeed%20Indicator.-Master.PDF - Photo 7. Horizontal stabilizer and elevator. (item 16, .PDF, 38 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338522&FileExtension=.PDF&FileName=Photo%207.%20Horizontal%20stabilizer%20and%20elevator.-Master.PDF - Photo 8. Elevator trim tab (fixed). (item 17, .PDF, 25 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338523&FileExtension=.PDF&FileName=Photo%208.%20Elevator%20trim%20tab%20(fixed).-Master.PDF - Photo 9. Elevator hinge attached to stabilizer. (item 18, .PDF, 37 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40338524&FileExtension=.PDF&FileName=Photo%209.%20Elevator%20hinge%20attached%20to%20stabilizer.-Master.PDF 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.