# NTSB DEN07FA008: McDonnell Douglas MD-90-30, N906DA, Denver, CO, October 12, 2006 - Type: NTSB accident investigation - Classification: Accident · No injuries · Field investigation · Final report - Date: October 11, 2006, 18:27 local (Oct 12, 2006, 00:27 UTC) - Place: Denver, CO - Coordinates: 39.861667, -104.673057 - Nearby events: https://openairdocs.org/map.md?lat=39.8617&lon=-104.6731&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 155 uninjured - Status: Completed, report April 25, 2007 - Report: Approved by Office Director - Parties: FAA Flight Standards District Office - NTSB case key (mKey): 64681 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN07FA008 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/64681/pdf - Page: https://openairdocs.org/ntsb/DEN07FA008 ## Probable cause A fractured nose gear assembly spray deflector that blocked the nose gear from extending during landing, and resulted in an intentional nose gear up landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - vfr pattern - final approach - landing gear,nose gear assembly - fractured (cause) - landing gear,nose gear assembly - overload - Wheels up landing, landing - flare/touchdown - wheels up landing - intentional, flightcrew - landing gear,nose gear assembly - blocked(total) (cause) - terrain condition - runway ## Analysis When the landing gear was extended on final approach, the nose gear UNSAFE light illuminated. A low fly-by was made, and control tower personnel confirmed that the nose gear appeared to be retracted. After consulting with the company's maintenance department, unsuccessful attempts were made to lower the nose gear, and a nose gear-up landing was made. Postaccident examination revealed that the nose landing gear center spray deflector had fractured and rotated, preventing gear extension. The spray deflector is designed to deflect water and other runway material kicked up by the nose wheel away from the rear-mounted engines which could cause flameouts and engine damage. About one-third of the spray deflector was broken off. Laboratory examination of the deflector revealed the fracture was typical of overstress. The nose gear doors were scraped, and the aluminum skin just aft of the nose wheel well was scraped through, exposing 5 longerons and 6 stringers, compromising the pressure vessel. ## Factual narrative HISTORY OF FLIGHT On October 11, 2006, at 1827 mountain daylight time, a McDonnell Douglas MD-90-30, N906DA, registered to and operated by Delta Air Lines, Inc., as Flight 1636, and piloted by an airline transport certificated pilot, was substantially damaged when the nose landing gear failed to extend and the crew was forced to make a nose gear-up landing at Denver International Airport (DEN), Denver, Colorado. Visual meteorological conditions (VMC) prevailed at the time of the accident. The scheduled domestic passenger flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 121, and an instrument flight rules (IFR) flight plan had been filed. The captain, first officer, three flight attendants and 150 passengers were not injured. The flight originated at Salt Lake City International Airport (SLC), Salt Lake City, Utah, at 1703 and was en route to DEN. According to the crew's written statements, the takeoff and en route portions of the flight were uneventful. When the landing gear was extended on final approach to DEN, the nose gear UNSAFE light illuminated. A low fly-by was made and control tower personnel confirmed that the nose gear appeared to be retracted. After consulting with the company's maintenance department, attempts were made to lower the nose gear but they were unsuccessful. After the flight attendants briefed the passengers, a nose gear-up landing was made on runway 16R. As the nose section skidded on the runway, a small fire erupted in the nose wheel well area and self-extinguished. No emergency evacuation was ordered. Passengers deplaned through the cabin door and were bussed to the terminal. DAMAGE TO AIRCRAFT After the airplane had been removed from the runway and towed to a secured area, Delta maintenance personnel found that the nose landing gear center spray deflector had fractured and rotated, preventing gear extension (the spray deflector is designed to deflect water and other runway material kicked up by the nose wheel away from the rear-mounted engines which could cause flameouts and engine damage). About one-third of the spray deflector was broken off. The nose gear doors were scraped. The aluminum skin just aft of the nose wheel well was scraped through, exposing 5 longerons and 6 stringers. Two antennae and one drain mast were also broken off. The pressure vessel was compromised. PERSONNEL (CREW) INFORMATION The captain, age 50, held an airline transport pilot certificate with an airplane multiengine land rating, commercial privileges in airplanes single-engine land, and type ratings in the Douglas DC-9 and Lockheed L-382. He also held a flight engineer certificate, dated January 1, 1988, with a turbojet rating. His 1st-class airman medical certificate, dated September 1, 2006, contained no restrictions and limitations. He had logged 10,879 total flight hours, and 165 hours in the MD-90 in the previous 90 days. His last proficiency check was accomplished in the MD-90 on August 21, 2006. The first officer, age 37, held an airline transport pilot certificate with an airplane multiengine land rating, commercial privileges in airplanes single-engine land, and type ratings in the Douglas DC-9 and British Aerospace BAe-3100. He also held a flight engineer certificate, dated March 18, 1999, with a turbojet rating. His 1st-class airman medical certificate, dated December 16, 2005, contained no restrictions and limitations. He had logged 3,762 total flight hours, and 191 hours in the MD-90 in the previous 90 days. His last proficiency check was accomplished in the MD-90 on July 21, 2006. The three flight attendants had been trained and were certificated on the MD-90. AIRCRAFT INFORMATION The McDonnell Douglas Airplane Company built N906DL (s.n. 53386), a model MD-90-30, in 1995. It was powered by two International Aero V2528-D5 turbofan engines (serial number 020027, left; 020015, right), each rated at 28,000 pounds of thrust. The airplane was maintained under a continuous airworthiness maintenance program. The following inspections were performed: "A" Check September 22, 2006 31,605.9 hours 16,662 cycles "B" Check February 15, 2006 30,004.4 hours 15,726 cycles "C" Check February 15, 2006 30,004.4 hours 15,726 cycles "D" Check July 26, 2001 18,476.1 hours 9,899 cycles At the time of the accident, the airplane had accrued 31,746.9 hours and 16,739 cycles. METEOROLOGICAL INFORMATION Denver's ASOS (Automated Surface Observing System) recorded the following special METAR (Aviation Routine Weather Report) at 1837: Wind, 120 degrees at 5 knots; visibility, 10 statute miles (or greater); sky condition, few clouds at 7,000 feet, 10,000 feet scattered, 13,000 feet scattered, 20,000 feet scattered; temperature, 10 degrees Celsius (C.); dew point, 3 degrees C.; altimeter, 29.88 inches of Mercury. Remarks: Altocumulus standing lenticular clouds VC southwest through northwest. AERODROME INFORMATION DEN is located 16 miles northeast of downtown Denver, and is situated at an elevation of 5,431 feet msl (above mean sea level). The airport has 12 runways. N906DA landed on runway 16R (16,000 feet x 200 feet, concrete, grooved). FLIGHT RECORDERS The airplane was equipped with a cockpit voice recorder (CVR) and a digital flight data recorder (DFDR). The recorders were sent to NTSB's Vehicle Recorder Division in Washington, DC, for download and readout. Summary reports are attached to this report (see EXHBITIS). WRECKAGE AND IMPACT INFORMATION DEN operations officials examined runway 16R prior to it being reopened. They reported the airplane touched down approximately the 1,000-foot mark, and the nose section touched down at the 5,200-foot mark. A 15-inch x 7-inch portion of the nose gear door was found at the 5,500-foot mark. A 7-inch x 1-inch strip of metal and a 16-inch x 7-inch piece of nose gear door was found at the 5,900-foot mark. There was a piece of insulation and strap, 1.5-inch in diameter, at the 6,000-foot mark. At the 6,500-foot mark, there was a 2.5-inch x 5-inch piece of sheet metal. The airplane came to rest at the 7,200-foot mark. TESTS AND RESEARCH The National Transportation Safety Board's (NTSB) Materials Laboratory Division examined the nose gear spray deflector. According to the factual report (06-101), "The center deflector assembly was fractured at two locations separating the left side deflector. The fractures were located around the two bolts attaching the left side deflector to the center deflector assembly. Magnified optical examinations of both fractures uncovered uniformly rough, gray fracture features typical of overstress separations in aluminum castings. Fracture features and fracture orientations were consistent with downward bending loads on the left deflector. No indications of preexisting cracking or porosity were observed on the fractures." The report concluded that Brinell hardness values (100 and 121 HB) of the center deflector were "consistent with the specified alloy (cast aluminum C355) and heat treatment (T61 temper)." ADDITIONAL INFORMATION On the MD-90, the spray deflector assembly -- which is attached to the nose landing gear - is a composite and consists of a center deflector, two rear deflectors, two side deflectors, and two supports. The spray deflector assembly on the MD-88 is similar to that of the assembly on the MD-90, but is aluminum and has a single piece rear/side deflector, which attaches to the same center deflector assembly. Following this accident, Delta Air Lines inspected its fleet of 16 MD-90s and 120 MD-88s. One -- an MD-90, N903DA -- had large cracks in the spray deflector assembly, but the assembly had not failed completely. According to Delta's Engineering Report (2-458305-20), the cracking was the result "of an overload condition." Further investigation revealed that the "fracture mode ## Aircraft - Registration: [N906DA](https://openairdocs.org/deregistered/N906DA-2021-02-12), registration cancelled 2021-02-12, S/N 53386, built 1995 (OpenAirDocs) - Reported make and model: McDonnell Douglas MD-90-30 - Registry model: [Mcdonnell Douglas MD-90-30](https://openairdocs.org/model/mcdonnell-douglas-md-90-30) (registry code 3023690) (OpenAirDocs) - Registry engine: [IAE V2500SERIES](https://openairdocs.org/engine/iae-v2500series) (registry code 34601, turbo-jet) (OpenAirDocs) - Category: Airplane - Serial number: 53386 - Airframe hours: 31747 - Engines: International Aero Engines V2528-D5 28000 horsepower turbo fan - Damage: Substantial damage - Flight: Part 121 - Registered owner: Delta Air Lines, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, September 1, 2006 - Departed: SLC, Salt Lake City, UT - Destination: DEN, Denver, CO - Flight plan: IFR - Airport: DEN, Denver International Airport, runway 16R, 16,000 × 200 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: none; airline transport, commercial, flight engineer; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review August 1, 2006; seat: left; flight hours: 13,300 total, 165 in the last 90 days, 1 in the last 24 hours - Co-pilot; age 37; injuries: none; flight instructor, commercial, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review July 1, 2006; seat: rear; flight hours: 7,200 total, 191 in the last 90 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Dusk - Wind: 120° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 50 °F, dew point 37 °F - Altimeter: 29.87 inHg - Observed at: DEN ## 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 20061011021509A](https://openairdocs.org/incident/20061011021509A), Oct 11, 2006: Doug MD9030, Denver, CO, Substantial damage. (-23) Delta 1636 on a routine flight from kslc to kden encountered a nose gear malfunction on lowering the gear for landing @ den, leveled off at 1000' AGL,… 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.