# NTSB CHI06FA076: Cessna 421B, N920MC, Wheeling, IL, January 31, 2006 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: January 30, 2006, 18:29 local (Jan 31, 2006, 00:29 UTC) - Place: Wheeling, IL - Coordinates: 42.123611, -87.902221 - Nearby events: https://openairdocs.org/map.md?lat=42.1236&lon=-87.9022&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 4 fatal - Status: Completed, report July 25, 2007 - Report: Approved by Office Director - Parties: Teledyne Continental Motors, FAA, Dupage FSDO, Cessna Aircraft Company - NTSB case key (mKey): 63189 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI06FA076 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/63189/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=63189 - Page: https://openairdocs.org/ntsb/CHI06FA076 ## Probable cause The pilot's failure to maintain airspeed during the landing approach which led to an inadvertent stall and subsequent uncontrolled descent and impact with the ground. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of control - in flight, approach - vfr pattern - downwind - airspeed - not maintained, unknown (cause) - stall - inadvertent, unknown (cause) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - ground ## Analysis The airplane was destroyed and the occupants fatally injured when it impacted the ground during approach to landing. Examination of the airplane, its engines and propellers, revealed no anomalies that were determined to have existed prior to impact. The propellers were found to have been in their normal operating range and neither propeller was in a feathered position. The quill shafts of both engines showed evidence of damage due to the production of torque. A sound spectrum examination of audio transmissions showed signatures that both engines were operating during the last two radio transmissions from the airplane. Based on radar data, communications and meteorological information obtained during the investigation, the airplane was operating in visual meteorological conditions below an overcast layer of clouds. The radar data showed the airplane as it approached the airport and as it entered a left hand traffic pattern for runway 34. Radio communications confirmed that the airplane had been cleared for a left hand traffic pattern to runway 34. The radar data showed the airplane as it made a turn to the left while its speed decreased to about 82 knots calibrated airspeed as of the last received radar return. This radar return was about 0.1 nautical miles from the accident site and 0.8 nautical miles and 216 degrees from the approach end of runway 34. The airplane owner's manual listed stall speeds ranging from 81 to 94 knots calibrated airspeed for airplane configurations including gear and flaps up to gear down and flaps 15 degrees, and bank angles from 0 to 40 degrees. Flap position could not be determined because the flap chain had separated from the flap drive motor. The owner's manual also listed an approach speed of 103 knots. ## Factual narrative This narrative was modified on July17, 2007. HISTORY OF FLIGHT On January 30, 2006, at 1829 central standard time (CST), a Cessna model 421B, N920MC, piloted by a private pilot, was destroyed when it impacted the ground in Wheeling, Illinois. The airplane was in the landing traffic pattern for runway 34 at the Palwaukee Municipal Airport (PWK) when the accident occurred. The 14 CFR Part 91 business flight was operating in visual meteorological conditions and was on an instrument flight rules (IFR) flight plan. All four occupants were fatally injured. The airplane had departed from the Johnson County Executive Airport (OJC), Olathe, Kansas, about 1710. According to communication records, the airplane received an IFR clearance and departed OJC at 1710. The airplane continued its flight to the Chicago area where an ILS runway 16 approach to PWK was executed. The IFR flight plan was cancelled and the airplane was cleared to land on runway 34 at PWK. The airplane subsequently impacted the ground approximately 0.9 miles and 210 degrees from the approach end of runway 34 at PWK. PERSONNEL INFORMATION The individual listed as the pilot in command (PIC) on the aircraft flight plan held a private pilot certificate with single engine land, multiengine land, and instrument airplane ratings. He also held a second class medical certificate that was issued on January 24, 2005. The medical certificate included a restriction that the pilot wear corrective lenses. A review of the PIC's flight logbooks was conducted. Due to several mathematical errors that were discovered, re-totaling of the individual logbook entries was conducted. These totals revealed that the pilot had accumulated a total of 1,284.05 hours total flight experience including; 161.2 hours in single-engine airplanes, 1,052.65 hours in multiengine airplanes, and 70.2 hours in flight simulator devices. The records showed that 32.75 hours were logged in Cessna 421 airplanes. Of those 32.75 hours, 18.2 hours were obtained prior to the pilot having received the instruction required by 14 CFR 61.31 (g) to act as pilot in command of a pressurized airplane. In addition, of the 32.75 hours logged in Cessna 421 airplanes, 27.5 hours were obtained prior to the pilot having received dual instruction in a Cessna 421 airplane. A total of 5.25 hours of logged dual instruction in Cessna 421 airplanes was recorded in the pilot's logbook. Another occupant held a commercial pilot certificate with single engine land, multiengine land, and instrument airplane ratings. The single engine rating was limited to private pilot privileges. This pilot also held a third class medical certificate issued on November 10, 2005. The medical certificate included a restriction that the pilot wear corrective lenses for near vision. On his most recent application for his airman medical certificate, he reported having in excess of 2,000 hours of flight experience including 40 hours in the preceding 6 months. The pilot's flight logbooks were not reviewed. No determination could be made as to which front seat occupant was manipulating the controls prior to or at the time of the accident. AIRCRAFT INFORMATION The airplane was a Cessna model 421B, serial number 421B0884. It was a twin-engine, low-wing, retractable gear airplane. The airplane was equipped with wing and tail de-icing boots and propeller anti-ice and was approved for flight into known icing conditions. A review of the airframe logbooks revealed that the airplane had accumulated 5,436.8 hours total time in service as of the most recent annual inspection dated December 28, 2005. The airplane was powered by 2 Teledyne Continental Motors model GTSIO-520-H engines. Each geared engine was rated to produce 375 horsepower at 2,275 propeller rpm. Each engine maintenance logbook was reviewed. During the review, a mathematical error relating to the accumulated time on the left engine was found. After taking this mathematical error into account it was found that the left engine, serial number 267029-R, had accumulated 1,782.8 hours total time and 455.5 hours since overhaul as of the December 28, 2005, annual inspection. The right engine, serial number 267035-R, had also accumulated 1,782.8 hours total time and 455.5 hours since overhaul as of the December 28, 2005, annual inspection. According to Cessna Aircraft company records, the airplane was originally purchased from Cessna on March 21, 1975. Federal Aviation Administration (FAA) registration records showed that the airplane was purchased on August 27, 2004, by the hotel company owned by the pilot rated passenger. On May 12, 2005, the airplane registration was transferred to HK Golden Eagle, Inc. The pilot rated passenger was listed on the FAA registration documents as the president/secretary of HK Golden Eagle, Inc. METEOROLOGICAL INFORMATION The National Weather Service (NWS) Weather Depiction Chart for 1900 CST January 30, 2006, depicted a region of IFR conditions over northern Indiana and southwestern Michigan. Surrounding this area was an area of marginal visual flight rules (MVFR) conditions that covered portions of Wisconsin, Illinois, Indiana, and Michigan that included the accident site. The NWS Current Icing Potential for 1800 CST depicted a probability of icing conditions over the Chicago area which ranged from about 10 percent at 3,000 feet, to about 70 percent at 5,000 feet. Several pilot reports of icing were recorded in the hours surrounding the accident time. One aircraft reported moderate rime icing between 2,500 and 7,000 feet about 15 minutes prior to the accident time. PWK is equipped with an Automated Surface Observation System (ASOS) and is augmented by NWS certified weather observers. The surface observations at PWK reported a mixture of freezing precipitation and snow that started at 0649 CST and turned to light snow and mist which continued on and off through 1648 CST. No major accumulation of ice or snow was reported during the period. The observations surrounding the accident time were as follows: At 1753 CST, wind from 310 degrees at 13 knots, visibility unrestricted at 10 statute miles, ceiling broken at 2,000 feet above ground level (AGL), overcast at 2,800 feet AGL, temperature -1 degrees Celsius (C), dew point temperature -4 degrees C, altimeter setting 29.81 inches of Mercury (Hg). Remarks: automated observation system, sea level pressure 1010.0 hectopascals (hPa), 6-hour precipitation less than 0.01 inches, temperature -0.6 degrees C, dew point -3.9 degrees C, 12-hour maximum temperature 2.8 degrees C, 12-hour minimum temperature -0.6 degrees C, 3-hour pressure tendency risen 1.9-hPa. At 1836 CST, wind from 310 degrees at 9 knots, visibility unrestricted at 10 statute miles, ceiling overcast at 2,100 feet AGL, temperature -1 degrees C, dew point temperature -4 degrees C, altimeter setting 29.83 inches of Hg. Remarks: automated observation system, aircraft mishap. COMMUNICATIONS Records indicate that an individual called the Columbia Automated Flight Service Station (AFSS) at 1543, filed an IFR flight plan, and obtained weather information for a flight from OJC to PWK. The caller identified N920MC as the registration number of the airplane when filing the flight plan. The caller also indicated that he was the pilot in command and provided his name and telephone number to the AFSS briefer when he filed the flight plan. The complete transcript of this communication is included in the docket material associated with this report. At 1710, the accident airplane departed OJC and radio contact with air traffic control was established. Between 1710 and 1826, the airplane continued its flight to PWK while maintaining communications with the appropriate ATC facilities. At 1826, communication between the aircraft and the PWK air traffic control tower (ATCT) was established. The following is a transcript of radio co ## Aircraft - Registration: [N920MC](https://openairdocs.org/deregistered/N920MC-2017-05-23), registration cancelled 2017-05-23, S/N 421B0884, built 1974 (OpenAirDocs) - Reported make and model: Cessna 421B - Registry model: [Cessna 421B](https://openairdocs.org/model/cessna-421b) (registry code 2076014) (OpenAirDocs) - Registry engine: [Continental TSIO-520 series](https://openairdocs.org/engine/continental-tsio-520-series) (registry code 17040, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 421B0884 - Airframe hours: 5437 - Engines: Continental GTSIO-520-H 375 horsepower reciprocating - Damage: Destroyed - Fire: On-Ground - Flight: Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, December 1, 2005 - Departed: OJC, OLATHE, KS - Destination: PWK, Wheeling, IL - Flight plan: IFR - Airport: PWK, Palwaukee Muni, runway 34, 5,000 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 59; injuries: fatal; private; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review October 1, 2004; seat: left; toxicology performed; flight hours: 1,284 total, 33 in this make and model - Other flight crew; age 61; injuries: fatal; commercial, private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; seat: right; toxicology performed; flight hours: 2,000 total ## Weather - Conditions: Visual (VMC), Night - Wind: 310° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: 2,100 ft overcast - Temperature: 30 °F, dew point 25 °F - Altimeter: 29.81 inHg - Observed at: PWK, 1 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 20060130007309A](https://openairdocs.org/incident/20060130007309A), Jan 30, 2006: Cessna 421B, Chicago/Wheelin, IL, Destroyed, 4 fatal. (-23) During normal night landing when turning from downwind to base the aircraft entered a stall with a left turn impacting near vertical. Landing gear was… ## Docket (45 files) The files NTSB released with the investigation on March 30, 2007, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=63189. 32.9 MB in all. - Sound Spectrum Study - Specialist's Factual Report of Investigation (item 1, .PDF, 14 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40270359&FileExtension=.PDF&FileName=Sound%20Spectrum%20Study%20-%20Specialist%27s%20Factual%20Report%20of%20Investigation-Master.PDF - Meteorology 5 - Factual Report of Group Chairman (item 2, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40263256&FileExtension=.PDF&FileName=Meteorology%205%20-%20Factual%20Report%20of%20Group%20Chairman-Master.PDF - Medical Records Information (item 3, .PDF, 9 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40270274&FileExtension=.PDF&FileName=Medical%20Records%20Information-Master.PDF - Witness Reports (item 4, .PDF, 170 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274334&FileExtension=.PDF&FileName=Witness%20Reports-Master.PDF - Radar Track Plot (1) (item 5, .PDF, 545 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274335&FileExtension=.PDF&FileName=Radar%20Track%20Plot%20(1)-Master.PDF - Radar Track Plot (2) (item 6, .PDF, 391 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274336&FileExtension=.PDF&FileName=Radar%20Track%20Plot%20(2)-Master.PDF - Radar Track Plot (3) (item 7, .PDF, 28 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274337&FileExtension=.PDF&FileName=Radar%20Track%20Plot%20(3)-Master.PDF - Radar Track Plot (4) (item 8, .PDF, 13 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274338&FileExtension=.PDF&FileName=Radar%20Track%20Plot%20(4)-Master.PDF - ATC Communication Summaries & Transcripts (item 9, .PDF, 205 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274339&FileExtension=.PDF&FileName=ATC%20Communication%20Summaries%20%26%20Transcripts-Master.PDF - Flight Service Station Briefing Transcript & Flight Plan Information (item 10, .PDF, 181 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274340&FileExtension=.PDF&FileName=Flight%20Service%20Station%20Briefing%20Transcript%20%26%20Flight%20Plan%20Information-Master.PDF - Controller Statement (item 11, .PDF, 57 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274341&FileExtension=.PDF&FileName=Controller%20Statement-Master.PDF - Aircraft Information (item 12, .PDF, 35 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274342&FileExtension=.PDF&FileName=Aircraft%20Information-Master.PDF - Owners Manual Excerpts (item 13, .PDF, 190 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274349&FileExtension=.PDF&FileName=Owners%20Manual%20Excerpts-Master.PDF - Propeller Teardown (item 14, .PDF, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274351&FileExtension=.PDF&FileName=Propeller%20Teardown-Master.PDF - Toxicological Reports (item 15, .PDF, 173 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274352&FileExtension=.PDF&FileName=Toxicological%20Reports-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 16, .PDF, 331 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274353&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 17, .PDF, 123 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274354&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Photo 1. View of Tail Surfaces (item 18, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274355&FileExtension=.PDF&FileName=Photo%201.%20%20View%20of%20Tail%20Surfaces-Master.PDF - Photo 2. Overall View of Main Wreckage (item 19, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274356&FileExtension=.PDF&FileName=Photo%202.%20%20Overall%20View%20of%20Main%20Wreckage-Master.PDF - Photo 3. Overall View of Main Wreckage (item 20, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274357&FileExtension=.PDF&FileName=Photo%203.%20%20Overall%20View%20of%20Main%20Wreckage-Master.PDF - Photo 4. Right Propeller at Accident Scene (item 21, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274358&FileExtension=.PDF&FileName=Photo%204.%20%20Right%20Propeller%20at%20Accident%20Scene-Master.PDF - Photo 5. Left Propeller at Accident Scene (item 22, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274359&FileExtension=.PDF&FileName=Photo%205.%20%20Left%20Propeller%20at%20Accident%20Scene-Master.PDF - Photo 6. View of Main Wreckage (item 23, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274360&FileExtension=.PDF&FileName=Photo%206.%20%20View%20of%20Main%20Wreckage-Master.PDF - Photo 7. Right Engine at Accident Scene (item 24, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274361&FileExtension=.PDF&FileName=Photo%207.%20%20Right%20Engine%20at%20Accident%20Scene-Master.PDF - Photo 8. Overall View of Wreckage (item 25, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274362&FileExtension=.PDF&FileName=Photo%208.%20%20Overall%20View%20of%20Wreckage-Master.PDF - Photo 9. Left Engine at Accident Scene (item 26, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274363&FileExtension=.PDF&FileName=Photo%209.%20%20Left%20Engine%20at%20Accident%20Scene-Master.PDF - Photo 10. Left Engine Prepared for Disassembly (item 27, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274364&FileExtension=.PDF&FileName=Photo%2010.%20%20Left%20Engine%20Prepared%20for%20Disassembly-Master.PDF - Photo 11. Left Engine Reduction Gear Section (item 28, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274365&FileExtension=.PDF&FileName=Photo%2011.%20%20Left%20Engine%20Reduction%20Gear%20Section-Master.PDF - Photo 12. Left Engine Internal View (item 29, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274367&FileExtension=.PDF&FileName=Photo%2012.%20%20Left%20Engine%20Internal%20View-Master.PDF - Photo 13. Left Engine Cylinders & Pistons (item 30, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274369&FileExtension=.PDF&FileName=Photo%2013.%20%20Left%20Engine%20Cylinders%20%26%20Pistons-Master.PDF - Photo 14. Left Engine Cylinders and Pistons (item 31, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274370&FileExtension=.PDF&FileName=Photo%2014.%20%20Left%20Engine%20Cylinders%20and%20Pistons-Master.PDF - Photo 15. Left Engine Quill Shaft (item 32, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274371&FileExtension=.PDF&FileName=Photo%2015.%20%20Left%20Engine%20Quill%20Shaft-Master.PDF - Photo 16. Left Engine Quill Shaft - Detail View (item 33, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274372&FileExtension=.PDF&FileName=Photo%2016.%20%20Left%20Engine%20Quill%20Shaft%20-%20Detail%20View-Master.PDF - Photo 17. Right Engine (item 34, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274373&FileExtension=.PDF&FileName=Photo%2017.%20%20Right%20Engine-Master.PDF - Photo 18. Right Engine Internal View (item 35, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274374&FileExtension=.PDF&FileName=Photo%2018.%20%20Right%20Engine%20Internal%20View-Master.PDF - Photo 19. Right Engine Reduction Gears (item 36, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274375&FileExtension=.PDF&FileName=Photo%2019.%20%20Right%20Engine%20Reduction%20Gears-Master.PDF - Photo 20. Right Engine Pistons & Cylinders (item 37, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274376&FileExtension=.PDF&FileName=Photo%2020.%20%20Right%20Engine%20Pistons%20%26%20Cylinders-Master.PDF - Photo 21. Right Engine Pistons & Cylinders (item 38, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274377&FileExtension=.PDF&FileName=Photo%2021.%20%20Right%20Engine%20Pistons%20%26%20Cylinders-Master.PDF - Photo 22. Right Engine Crankshaft and Connecting Rods (item 39, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274378&FileExtension=.PDF&FileName=Photo%2022.%20%20Right%20Engine%20Crankshaft%20and%20Connecting%20Rods-Master.PDF - Photo 23. Right Engine Quill Shaft (item 40, .PDF, 422 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274379&FileExtension=.PDF&FileName=Photo%2023.%20%20Right%20Engine%20Quill%20Shaft-Master.PDF - Photo 24. Right Engine Quill Shaft Magnaflux View (item 41, .PDF, 443 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274380&FileExtension=.PDF&FileName=Photo%2024.%20%20Right%20Engine%20Quill%20Shaft%20Magnaflux%20View-Master.PDF - Security Video Still 1 (item 42, .PDF, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274381&FileExtension=.PDF&FileName=Security%20Video%20Still%201-Master.PDF - Security Video Still 2 (item 43, .PDF, 80 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274382&FileExtension=.PDF&FileName=Security%20Video%20Still%202-Master.PDF - Security Video Still 3 (item 44, .PDF, 78 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274384&FileExtension=.PDF&FileName=Security%20Video%20Still%203-Master.PDF - Security Video Still 4 (item 45, .PDF, 39 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40274385&FileExtension=.PDF&FileName=Security%20Video%20Still%204-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.