# NTSB LAX97LA061: McDonnell Douglas MD-600N, N630N, Flagstaff, AZ, November 21, 1996 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: November 21, 1996, 09:01 local (16:01 UTC) - Place: Flagstaff, AZ - Coordinates: 35.22969, -111.719329 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.2297&lon=-111.7193&mi=10 - Phase of flight: [Other](https://openairdocs.org/ntsb-phases/800) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 2, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 29697 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX97LA061 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/29697/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=29697 - Page: https://openairdocs.org/ntsb/LAX97LA061 ## Probable cause The pilot's inattention to the altitude and inadvertent late entry into an autorotation maneuver below the established minimum test altitude with a helicopter operating at maximum gross weight in a high density altitude environment that led to a subsequent hard landing. Contributing were the lack of positive communications between ground test personnel and the pilot regarding the low altitude, and the lack of accurate in-flight and ground altimeter equipment. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Abrupt maneuver, other - Hard landing, landing - flare/touchdown - weather condition - high density altitude (contributing factor) - aircraft weight and balance - attempted, manufacturer (contributing factor) - flight/nav instruments,altimeter - inadequate (contributing factor) - altitude - inattentive, pilot in command (cause) - acft/equip,inadequate instrument display, production/design personnel (contributing factor) - air/ground communications - inaccurate, pilot in command (cause) - air/ground communications - disregarded, ground personnel (cause) ## Analysis The helicopter was being flight tested to validate certification criteria for height velocity curves at a maximum gross weight and zero airspeed at a high density altitude airport. On the fourth test profile, the pilot allowed the aircraft to descend below the target altitude of 800 feet agl by almost 70 feet. The ground test engineers observed the drift down and didn't advise the pilot because they assumed he had already begun the autorotation after he had made the 3 second call, and also they believed their ground equipment was inaccurate. The pilot delayed the autorotation for about 8 to 12 seconds and then lowered the collective. The aircraft landed hard exceeding the maximum load for the landing gear system. The horizontal speed at touchdown was 52 knots instead of the target speed of 65 knots. The test helicopter was equipped with standard analog altimeters with pointers that have a lag time instead of the more accurate real time digital altimeters. ## Factual narrative On November 21, 1996, at 0901 hours mountain standard time, a McDonnell Douglas (MD) prototype experimental helicopter, MD-600N (NOTAR), N630N, landed hard during a local test flight at the airport in Flagstaff, Arizona. Visual meteorological conditions existed at the time. The aircraft sustained substantial damage and the pilot was not injured. This aircraft was involved in a similar accident with the same pilot at the same location during flight tests on 11/04/96 (LAX-97-L-A034). According to the operator, the test pilot was performing a series of height velocity curve autorotations at maximum gross weight (4,100 pounds) at various altitudes and at zero airspeeds between 800 to 1,000 feet above the ground (agl). During touchdown on the fourth autorotation, the helicopter contacted the runway and displaced both skids with the right skid separating from the aircraft at the brace assembly connecting bolt hole. The fuselage was buckled and cracked along the right side and the bottom of the fuselage. The investigation revealed that the three previous test point autorotations were conducted at: 1,000 feet agl at 40 knots airspeed; 1,000 feet, 0 airspeed; and at 850 feet, 0 airspeed. There were no reported problems with these tests. According to MD engineers, the first two test points had "mild touchdown rates" (less than 1.5 g's and less than 5 feet per second). The touchdown rate for the third data point indicated a 1.75 g or 5.2 feet per second. It was discovered (after the accident) that the actual entry for this test was begun at 810 feet, instead of the 850 foot intended altitude. On the fourth test point autorotation, the test pilot was to be at an entry altitude of 800 feet agl and zero airspeed. Prior to entry, the pilot radioed a standard 3 second call to the ground crew that he was about to begin the test run. According to MD ground test data personnel reviewing the instrumentation plots, the entry did not occur until 8 to 12 seconds after the pilot's initial call. During this time, the aircraft had drifted down approximately 70 to 730 feet agl. A review of the video recording indicated the helicopter contacted the runway with the aft portion of the skids. The touchdown rate was about 4.0 g's or 13.5 feet per second. The design limit for this landing gear (skid) system was 6.5 feet per second. According to the pilot, the autorotation looked very similar to the previous data point until touchdown. At touchdown, the right gear collapsed and the helicopter dropped onto its right side. He stated the touchdown speed was approximately 45 knots. According to the test data, the horizontal speed did not get above 60 knots indicated airspeed, whereas, the other previous data points had horizontal speeds over 64 knots. The test data for this autorotation indicated a speed of 52 knots at touchdown. The investigation revealed the helicopter was equipped with a standard barometric pressure altimeter and a radar altimeter that was recently calibrated to a + or - 10 feet. Neither of these altimeters provide a digital readout and the altitude seen by the pilot is the needle position (analog) on the gauge. According to MD, there were no other precision instruments available to assist the pilot with altitude readout. Ground personnel monitoring the altimeter strip chart, which they had known to be inaccurate, noticed the aircraft "drift down" about 50 feet and assumed the pilot had already lowered the collective to begin the test after he had made the 3 second call. They did not inform the pilot of their observations. As a result of this accident and others, MD reduced the maximum operating gross weight to 3,650 pounds and installed a digital altimeter in the cockpit. The McDonnell Douglas Helicopter Company has claimed an exemption from public disclosure of the information contained in their accident report as privileged and confidential. ## Aircraft - Registration: [N630N](https://openairdocs.org/aircraft/N630N), registered now, S/N 0004F, built 1984 (OpenAirDocs) - Reported make and model: McDonnell Douglas MD-600N - Registry model: [Hughes 369F](https://openairdocs.org/model/hughes-369f) (registry code 4470708) (OpenAirDocs) - Registry engine: [Rolls-Royce 250-C47 series](https://openairdocs.org/engine/rolls-royce-250-c47-series) (registry code 54235, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 0004F - Airframe hours: 1985 - Engines: Allison 250-C47M 808 horsepower turbo shaft - Damage: Substantial damage - Flight: Part 91 - Registered owner: Mcdonnell Douglas - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, April 26, 1996, 88 hours before - Departed: FLG - Airport: Flagstaff Pulliam, runway 21, 7,000 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 48; airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 10,342 total, 1,194 in this make and model, 8,145 as pilot in command, 113 in the last 90 days, 56 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 50 statute miles - Lowest ceiling: none - Temperature: 37 °F - Altimeter: 29.00 inHg ## 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 19961121039479A](https://openairdocs.org/incident/19961121039479A), Nov 21, 1996: Hughes 369FF, Flagstaff, AZ, Substantial damage. High velocity autorotations test. Impacted runway. Bent seperated skids. Began test too low. Low airspeed. Weight. ## Other investigations on N630N (2) 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. - [NTSB LAX04CA122](https://openairdocs.org/ntsb/LAX04CA122), Feb 12, 2004: McDonnell Douglas 369FF (N630N), Mesa, AZ, substantial damage. Probable cause: the pilot's inadequate compensation for the wind gusts and subsequent failure to maintain directional control of the helicopter, which resulted in a hard landing. A contributing factor was a wind… - [NTSB LAX97LA034](https://openairdocs.org/ntsb/LAX97LA034), Nov 4, 1996: McDonnell Douglas MD-600 (N630N), Flagstaff, AZ, substantial damage. Probable cause: An uncommanded main rotor blade to tail boom contact due to a 'blowback' phenomena after a successful preplanned autorotation by the pilot to a high density altitude airport with a test aircraft… ## Docket (3 files) The files NTSB released with the investigation on August 13, 1997, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=29697. 673 KB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2 (item 1, .PDF, 526 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40390003&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1%2F2-Redacted.PDF - Reports from Federal Agencies - FAA (item 2, .PDF, 107 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40390005&FileExtension=.PDF&FileName=Reports%20from%20Federal%20Agencies%20-%20FAA-Redacted.PDF - MD600 Accident Review (item 3, .PDF, 40 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40390006&FileExtension=.PDF&FileName=MD600%20Accident%20Review-Redacted.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.