# NTSB CHI03IA066: Bombardier BD 100-1A10, Wichita, KS, February 5, 2003 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: February 4, 2003, 18:00 local (Feb 5, 2003, 00:00 UTC) - Place: Wichita, KS - Location: 37.6922° N, 97.3375° W: Placed by OpenAirDocs: center of Wichita, KS, within about 7 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=37.6922&lon=-97.3375&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report May 30, 2006 - Report: Approved by Office Director - Parties: Bombardier Aerospace, Transportation Safety Board of Canada, U.S. Air Force Research Laboratory, Avionics Instruments Incorporated, Federal Aviation Administration, AAI-100 - NTSB case key (mKey): 56480 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI03IA066 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/56480/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=56480 - Page: https://openairdocs.org/ntsb/CHI03IA066 ## Probable cause The uninterrupted current overload of the cabin outlet system static inverter leading to ignition and sustained fire. The cause of the initiating overload condition could not be determined. Contributing factors were the lack of adequate current overload protection for the static inverter due to a failure to adequately assess fire/smoke hazards of the inverter in this installation and the absence of timely fire annunciation to the flight crew. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Fire, cruise - acft/equip,inadequate design, manufacturer (contributing factor) - insufficient standards/requirements, manufacturer (contributing factor) - electrical system,inverter - fire (cause) - inverter - inadequate (contributing factor) - fluid,hydraulic - contamination,other than water - insufficient standards/requirements, faa(organization) (contributing factor) - electrical system - inadequate (cause) ## Analysis The experimental airplane returned from a test flight with evidence of an in-flight inverter fire discovered during a post flight inspection. The test flight was part of a new airplane certification test program and was to evaluate the airplane's audio design/flight deck audio system. The flight crew did not receive any fire warning indications in-flight and neither they or the test crew members noted any smoke or odors associated with burning during the flight. The inverter was located in the aft equipment bay, aft of the rear pressure bulkhead. The area within which the inverter was located was equipped with fire detection and an airplane circuit breaker for the system. The airplane circuit breaker for the inverter was not tripped. Subsequent testing demonstrated that the circuit breaker operated within specification limits. Inspection of the airplane revealed the presence of hydraulic fluid below and in the inverter tray. Examination of the inverter and fluid susceptibility testing confirmed the presence of Skydrol hydraulic fluid within the inverter. The inverter manufacturer reported that Skydrol intrusion, internal power circuit high voltages, operation at altitude, and drastic changes in temperature may have contributed to material degradation or deterioration or even possible dielectic breakdown, which resulted in the failure mode observed. Following this incident, the manufacturer reported that the inverter design was tested and confirmed that it met the fluid susceptibility requirements of DO-160C for Skydrol. A second examination of the inverter, performed by the United States Air Force Research Laboratory, was documented in a laboratory evaluation report. The failure analysis section of this report states that no root cause of failure could be found and noted that the majority of the thermal damage to the inverter was attributed to Joule heating from a sustained current overload. The examination also revealed the existence of numerous manufacturing deficiencies that would be classified as defects per Joint Industry Standard requirements for soldered electrical and electronic assemblies. The majority of these defects violated cleanliness, conformal coating, and soldering. The inverter manufacturer's FAA approved manufacturing requirements differ from those noted by the Air Force Research Laboratory and are based on its own internal design standards and practices as well as in-house workmanship standards derived from good industry practice and requirements contained in IPC-A-610C, "Acceptability of Electronic Assemblies". The inverter was part of a cabin outlet system considered non-essential under 14 CFR Part 25, Subpart F. Information contained in Advisory circular 25-10 regarding guidance for installation of miscellaneous, non-required equipment states. that circuit protective devices should be provided such that a fault in the nonrequired system does not cause a failure of a required system. Supplementing this guidance, AC 25-16, "Electrical Fault and Fire Prevention and Protection," states that in cases where internally faulted components will not cause automatic disconnection of their circuit protective devices before causing excess temperatures potentially resulting in fire, these electrical equipment should be provided with adequate backup protection (beyond the aircraft circuit breakers). In addition, the AC states that each installation of an electrical device should be assessed for its potential to generate fire or smoke under failure conditions. The inverter specified for this installation was a TSO-C73 certified article. The applicable TSO addresses short circuit and overload conditions to the extent that inverters continue producing power through these conditions, but it does not require circuit protection when these conditions are encountered. A design analysis of the inverter as installed in the cabin outlet system to consider failure conditions and corresponding hazards such as fire/smoke generation, in accordance with the related provisions of 14 CFR Part 25.1309, had not been performed by the aircraft manufacturer prior to this incident. As a result, additional requirements to address internal inverter circuit protection for this installation were not mandated by the aircraft manufacturer. Subsequent to this incident, a design analysis was performed by the airplane manufacturer. Correspondingly, the inverter manufacturer modified the inverter design to incorporate fuses on the power input lines to interrupt electrical power in the event a short circuit or overload failure condition develops inside the inverter. ## Factual narrative HISTORY OF FLIGHT On February 4, 2003, at 1800 central standard time, an experimental Bombardier BD-100-1A10, C-GJCV, operated by Bombardier Incorporated, returned from a test flight to Wichita-Mid Continent Airport, Wichita, Kansas, with evidence of an inverter fire within the tail cone. The airplane structure was undamaged. Visual meteorological conditions prevailed during the flight. The 14 CFR Part 91 flight was operating on a visual flight rules flight plan. The two airline transport pilots and two engineers were uninjured. The local flight originated at 1600. The airplane returned from a test flight, number 100, which was to evaluate the audio design/flight deck audio. During the flight, an engineer in the cabin was reported to have plugged his laptop computer into a cabin outlet and noticed that there was no electrical power shortly after takeoff. No smell or indication of smoke was noted by the pilots and engineers during the flight. The airplane landed without incident. Two of those aboard noticed a smell when they exited the airplane but did not associate the smell with the airplane. Ground personnel noticed a burn odor when the airplane was then towed into a hanger where soot in and around access panels of the left hand engine pylon and aft equipment bay was discovered. Further inspection revealed evidence that the inverter exhibited evidence of a fire. AIRCRAFT INFORMATION The BD-100-1A10 (Challenger 300), serial number 20004, received a United States Special Flight Authorization for research, development, compliance with an expiration October 17, 2003, as a part of a new aircraft certification program. The inverter was a Avionic Instruments Inc. (AI2) 2KVA, single-phase 60 Hz, model number 2E2000-1AC-1996, serial number (S/N) JC000002, static inverter. This make and model of inverter was not installed on the other BD-100-1A10 airplanes. The inverter consisted of three 667 VA power modules in parallel to provide a 60 Hz, 2 KVA output from a nominal 28 VDC input. Two of the three power modules used were also used in model number 1E1000-1A-2017 inverters. The inverter was installed in the aft equipment bay aft of the rear pressure bulk head between fuselage stations 685 - 724, center line 0 to right buttock line 15, and waterline 68 - 80. The inverter was attached directly to the airplane structure and was not mounted to a tray. The inverter was part of a nonessential airplane system (as defined by 14 CFR Part 25.1309 Equipment, Systems, and Installations) that supplied power to six interior cabin outlets and was not a part of any other aircraft system. A 1309 reliability and design analysis had not been performed on the system prior to the incident. The aft equipment bay was equipped with fire sensors and an airplane 100-amp cabin inverter circuit breaker, part number MS25361-100. Inverter S/N JC000002 was installed on October 25, 2002, and accumulated a total time of 278.2 hours. S/N JC000002 replaced inverter S/N JC000001 due to a failure of the unit on October 25, 2002. S/N JC000001 accumulated a total time of 185.9 hours at the time of failure. This unit was removed and sent to AI2 for examination which revealed there was chalk and conductive debris below the power semiconductors. Two of the power modules were working properly except for voltage breakdown from the output diodes of the DC/DC to the heat sink of the power module. WRECKAGE AND IMPACT INFORMATION The aft equipment bay access door was opened and the inverter displayed evidence of a fire and there was soot on and around the inverter. The area above the inverter was burnt and had curled paint. An area of about 1 inch by 1.5 inches was burned through. The entire floorboard area contained soot. An avionics unit to the left of the inverter contained soot but did not have burn damage. When this unit was removed from its tray, there was evidence of Skydrol hydraulic fluid erosion on the tray's painted surface. The inverter casing was wrinkled on the top and inboard sides. The upper portions had heavy soot deposit and an unknown white substance that protruded through some vent holes. There was no presence of Skydrol on the inverter. The bottom fuselage skin below and forward of the inverter contained Skydrol. The inverter was removed from the airplane and opened by Bombardier maintenance personnel in the presence of AI2 representatives and under the supervision of the Federal Aviation Administration (FAA). The unit's two upper circuit boards were noted to be burned. The inverter was then quarantined by Bombardier and sent to the FAA Manufacturing Inspection District Office (MIDO) having oversight of AI2. The airplane circuit breaker for the inverter powering the cabin electric outlets was not tripped. The circuit breaker was later tested during the investigation. TEST AND RESEARCH A query of the FAA's Service Difficulty Reporting Data, for the period from January 1, 1995 to February 7, 2003, for inverters in all aircraft make and models, yielded 243 reported occurrences relating to inverters. Of the 243 reported occurrences, 57 reported the presence of smoke. A second query of the FAA's accident/incident database was performed, for the period from January 1, 1974 to February 7, 2003. The query yielded 35 occurrences involving inverters. These database searches are included in the public docket of this report. Technical Service Order (TSO) C73, Static Electrical Power Inverter, dated December 18, 1963, stipulates under Part 514, the minimum performance standard and specification for material parts, and appliances used in aircraft. Subpart A of this part contained the general requirements applicable to all TSOs and subpart B contains the technical standards and specifications to which a particular product must conform. TSO-C73 cites the required performance standards under environmental test conditions 12 variables which include overload capacity, input overvoltage, and short circuit condition, as follows: Overload Capacity - The inverter shall be capable of withstanding, without damage, a current overload of at least 150 percent for a time duration of 5 minutes; Input voltage - The inverter shall be capable of withstanding, without damage, input overvoltage for a time period of 5 minutes while supplying full rated output power; Short Circuit Condition - The inverter shall be capable of withstanding, without damage, and output short circuit applied separately to each phase or simultaneously to all phases for a time period of one minute. Within 5 minutes after removal of the short circuit condition, the unit shall be energized and run cautiously for a period of at least 20 hours. During this period the unit shall, without degradation of performance, deliver the specified output. TSO-C73 has no requirement for short circuit or overload protection and has not been amended since its inception. The design and manufacturing standards followed in the manufacture of AI2 inverters were set forth by the company. The FAA Aircraft Certification Office bases their design approval on TSO-C73, and the FAA MIDO then uses the manufacturer’s standards in the conduct of its inspections. The inverter was sent to AI2 for examination under the oversight of the FAA. According to the AI2's final investigation summary report, "An outside test lab analysis confirmed the presence of Skydrol within the inverter. Skydrol intrusion, internal power circuit high voltages, operation at altitude, and drastic changes in temperature may have contributed to material degradation or deterioration or even possible dielectic breakdown, which resulted in the failure mode observed. The inverter design was tested and confirmed that is meets the Fluid Susceptibility requirements of DO-160C for Skydrol." "Avionic Instruments Inc. proposed the following design changes which will provide addi ## Aircraft - Registration: C-GJCV (not matched to a registry record) - Reported make and model: Bombardier BD 100-1A10 - Category: Airplane - Serial number: 20004 - Engines: Allied Signal AS907 6500 horsepower turbo fan - Damage: No damage - Fire: In-Flight - Flight: Flight test, Part 91 - Registered owner: Bombardier Aerospace - Airworthiness certificate: Special, Experimental (Special) - Departed: ICT, Wichita, KS - Destination: ICT - Flight plan: VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; injuries: none; airline transport, commercial; airplane ratings: multi-engine land; instrument ratings: helicopter; medical: class 1, unknown; seat: left - Co-pilot; injuries: none; commercial, airline transport; airplane ratings: multi-engine land, single-engine land; medical: class 1, unknown; seat: right ## Weather - Conditions: Visual (VMC), Day - Wind: 110° at 7 knots - Visibility: 10 statute miles - Temperature: 37 °F, dew point 21 °F - Altimeter: 30.13 inHg - Observed at: ICT ## Docket (10 files) The files NTSB released with the investigation on February 24, 2004, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=56480. 4.5 MB in all. - Weather Information (item 1, .PDF, 42 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204625&FileExtension=.PDF&FileName=Weather%20Information-Master.PDF - Advisory Circular 25-10 (item 2, .PDF, 307 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204626&FileExtension=.PDF&FileName=Advisory%20Circular%2025-10-Master.PDF - Technical Service Order TSO-C73 (item 3, .PDF, 691 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204627&FileExtension=.PDF&FileName=Technical%20Service%20Order%20TSO-C73-Master.PDF - SDR Accident Incident SDRs (item 4, .PDF, 256 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204628&FileExtension=.PDF&FileName=SDR%20Accident%20Incident%20SDRs-Master.PDF - SDRs Inverters (item 5, .PDF, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204630&FileExtension=.PDF&FileName=SDRs%20Inverters-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 6, .PDF, 294 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204631&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Photo 1. Install w sky hookup (item 7, .PDF, 215 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204632&FileExtension=.PDF&FileName=Photo%201.%20%20Install%20w%20sky%20hookup-Master.PDF - Photo 2. P2060028 (item 8, .PDF, 299 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204633&FileExtension=.PDF&FileName=Photo%202.%20%20P2060028-Master.PDF - Photo 3. sky in tray (item 9, .PDF, 237 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204634&FileExtension=.PDF&FileName=Photo%203.%20%20sky%20in%20tray-Master.PDF - Photo 4. top w cvr removed (item 10, .PDF, 280 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40204635&FileExtension=.PDF&FileName=Photo%204.%20%20top%20w%20cvr%20removed-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.