Thursday, February 16, 2017

Boeing 767-36NER, Omni Air International, N768NA: Accident occurred June 20, 2014 in Kabul, Afghanistan

Aviation Accident Final Report -  National Transportation Safety Board: https://app.ntsb.gov/pdf

Docket And Docket Items - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary -  National Transportation Safety Board: https://app.ntsb.gov/pdf

Additional Participating Entities:
Omni Air International
Boeing

IBT

NTSB Identification: DCA14FA122
Nonscheduled 14 CFR Part 121: Air Carrier operation of OMNI AIR INTERNATIONAL INC
Accident occurred Friday, June 20, 2014 in Kabul, Afghanistan
Probable Cause Approval Date: 01/23/2017
Aircraft: BOEING 767 36N, registration: N768NA
Injuries: 4 Minor, 77 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The flight experienced a tailstrike on landing resulting in substantial damage to the fuselage and aft pressure bulkhead. There were no injuries to the passengers; however, four of the 16 crewmembers received minor injuries.

According to the flight crew statements and recorder data, the landing reference speed for the approach was 145 knots. Due to the weather conditions, the flight crew added 10 knots to this for their approach speed due to the gusty weather conditions and conducted a visual approach using the visual approach slope indicator as guidance. As a result of the weather and gusty winds, airspeed fluctuated during the approach between 162 knots and 138 knots and engine thrust varied accordingly between about 86% N1 and 40% N1 on approach.

The captain stated that the flight was on speed and glide path at 500 feet above the ground but at about 200 feet above the ground, the flight started to move above the glide path and airspeed started to increase. To compensate, the captain reduced engine power and then heard a "sink rate" aural alert when passing through about 50 feet. Flight recorder data indicated the engine N1 decreased to 40%, with throttles at forward idle position, at about 110 feet above the ground, and remained there until after touchdown. The airplane touched down at 140 knots and a nose up pitch attitude of 8.9 °, increasing to 9.5° immediately after touchdown. 

Guidance included in the operator's training manuals indicated that normal touchdown attitude should be between 4 and 6 degrees nose up. Additionally, guidance indicated that thrust should be managed on approach to maintain reference speed, plus any wind additive, until the beginning of the flare. After reaching the flare, thrust levers should be retarded smoothly to idle with main gear touchdown ideally occurring simultaneously with thrust levers reaching idle.

An analysis of calculated vertical and horizontal wind effect indicated an existing updraft transitioned to a downdraft and a headwind component transitioned to a tailwind component during the last 5 seconds prior to touchdown.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
the early reduction of engine thrust that resulted in an excessive sink rate and nose high pitch attitude during the landing flare.

Contributing to the accident was a significant change in the vertical and horizontal wind components just prior to touchdown.

HISTORY OF FLIGHT

On June 20, 2014, about 1936 local time, a Boeing 767-36N, N768NA, operated by Omni Air International, experienced a tail strike during landing on runway 29 at Kabul International Airport (KBL), Kabul, Afghanistan. The flight originated from Bucharest International Airport (OTP), Bucharest, Romania and was operated as a non-scheduled charter under Title 14 Code of Federal Regulations Part 121. Four of the 16 crewmembers received minor injuries and none of the 65 passengers were injured. The aircraft was substantially damaged. In accordance with ICAO Annex 13, the Afghanistan Ministry of Transportation and Civil Aviation (MoTCA) delegated the investigation to the NTSB.

The flight departed OTP at 1322 local time with an expected enroute flight time of 4 hours 25 minutes to KBL. The captain was the pilot flying and occupied the left pilot seat.

During the descent, the crew completed the descent checklist and conducted an approach briefing, planning an RNAV approach to runway 29 and briefed a speed of "145." During the approach, the crew configured the airplane with gear down and full flaps and noted that the VNAV system was not indicating a vertical path.

At 1932:29 the first officer (FO) contacted the tower to request a wind check and the tower controller confirmed the flight was cleared to land and reported wind as 010 degrees at 18 gusting to 20. The captain (CA) then disengaged the autopilot and noted the airplane was slightly low and he was correcting.

After descending through 1000 feet, the CA noted they were on glide path and the FO requested another wind check. The tower controller advised wind was 360 degrees at 20 gusting to 40.

At 1935:02 the CVR recorded an automated callout of "500" and the CA noted they were slightly high and correcting. According to crew statements, approximately 200 feet above landing, the CA reduced power to correct from being above glide path and slightly fast. The crew stated that soon after passing 100 feet an automated "sink rate" callout was heard.

The CA stated that he increased power and started to flare and as the crew sensed the airplane drop, he increased pitch attitude to arrest the sink rate but landed hard and over rotated in the flare. 

After landing, the tower controller reported observing some sparks and cleared the flight to taxi to parking.

INJURIES TO PERSONS

There were no injuries to the 65 passengers and 12 of the 16 crewmembers. Four crewmembers received minor injuries.

DAMAGE TO AIRPLANE

The airplane was substantially damaged by deformation and wear due to runway contact resulting in structural damage to the fuselage skin, stringers, and frames. The skin on the lower fuselage was worn through to structure exhibiting signs of loss of material and multiple see-through holes and cracks over a 25 foot length from station 1395 rearward to station 1417. Internal damage to the frame included multiple damaged stiffeners and cracked web from frame station 1395 rearward to station 1562. Five bays were damaged at the lower end of the aft pressure bulkhead at station 1582, the web was deformed and the lower frame was bent.

PERSONNEL INFORMATION

The flight crew consisted of two pilots, two relief pilots and twelve additional crewmembers.

The captain, age 62, completed initial B-767 training in April 2012. The captain reported approximately 16,335 hours total time, including about 13,730 hours as pilot-in-command and 865 hours in the B-767. There were no records or reports of any previous aviation incidents or accidents involving the captain.

The captain held a valid Federal Aviation Administration (FAA) Airline Transport Pilot (ATP) certificate with type ratings for B-767/757, DC-10, G-IV, and CL-604 and a current FAA first-class medical certificate with a limitation indicating it was not valid after May 31, 2015. Company records indicated his most recent proficiency check was March 16, 2014. Training and proficiency checks were current and the company reported that the captain had no record of failures during company training events.

The first officer, age 33, reported approximately 5,500 hours total flight time and about 800 hours in the B-767; 700 of which was pilot-in-command time. There were no records or reports of any previous aviation incidents or accidents involving the first officer. He held a valid FAA ATP certificate with type ratings for the B-767/757, DC-10, and EMB-145 and an FAA first-class medical certificate with no limitations.

The first officer's training and proficiency checks were current and the company reported he had no failures recorded during company training events. He completed initial training in the B-767 in February 2012 and his most recent proficiency check was completed in February 2014

The captain and first officer had been flying together for the previous week schedule. The accident occurred on the first and only leg scheduled for the day following a 57 hour and 43 minute rest period.

AIRCRAFT INFORMATION

N768NA, serial number 29898, was a Boeing 767-36N manufactured in 1999 equipped with two GE CF6-80 engines. The company reported that the airplane had about 44,687 hours total time on the airframe and the last inspection was conducted on June 12, 2014. Recorded data and airline records indicated no relevant maintenance issues with the airplane. The airplane maximum certificated landing weight was 320,000 pounds and the actual landing weight was about 318,000 pounds.

METEOROLOGICAL INFORMATION

The KBL surface observation at 1920 local time reported wind from 110 degrees at 18 knots gusting to 32 knots, visibility 7000 meters, no significant clouds, temperature 26 degrees Celsius, dew point temperature minus 3 degrees Celsius, and altimeter setting 1010 hectopascals.

A tactical meteorological observation system on the field recorded the wind direction during the two minutes prior to landing as variable between 348 degrees to 064 degrees and the wind speed variable from 9.1 knots to 26.4 knots. Wind gust recorded during the same two-minute time period varied from 327 degrees to 349 degrees at 39.3 to 39.9 knots.

AERODROME INFORMATION

The Kabul International Airport (KBL) is located about 5 miles northeast of the city of Kabul, Afghanistan. The airport has 2 runways for military, commercial and general aviation. Runway 29 is asphalt, asphaltic concrete and tar macadam, 11,483 feet long, 164 feet wide with a touchdown zone elevation of 5,877 feet. The runway is served by a 4-light precision approach path indicator system (PAPI) with a 3 degree glide path on the right side of the runway, high intensity runway lights (HIRL), and an approach light system with sequenced flashers (ALSF-1).

FLIGHT RECORDERS

The cockpit voice recorder (CVR), a Honeywell 6022 SSCVR 120, serial number CVR120-03749, was removed from the airplane and downloaded at the NTSB Vehicle Recorder Laboratory. The CVR contained 2 hours, 5 minutes, 22 seconds of recording on two audio channels and about 30 minutes of recording on three audio channels. The audio quality of each channel was characterized as good, and the recording included events from in-flight operations, including approach and landing, and post-flight activities once the airplane arrived at the gate. Timing on the summary was established by correlating the CVR events to common events on the flight data recorder (FDR).

The FDR, a Honeywell SSFDR 980-4700-042, serial number SSFDR-2672, was removed from the airplane and downloaded at the NTSB Vehicle Recorders Laboratory. The recorder was found to be in good condition, and contained approximately 27 hours and 13 minutes of data. The data were extracted normally. Correlation of the FDR data to event local Kabul time, was established by using the recorded Universal Coordinated Time (UTC), Minutes, hours, and seconds parameters and applying an additional 4.5 hours offset to change from UTC to local time.

The airplane was equipped with a Honeywell MkV Enhanced Ground Proximity Warning System (EGPWS) Terrain Avoidance and Warning System (TAWS) which was removed from the airplane and downloaded at the NTSB Vehicle Recorders Laboratory with assistance from the manufacturer.

WRECKAGE INFORMATION

As a result of the damage to the lower aft fuselage and aft pressure bulkhead, the aircraft was ferried to another location where major repairs could be made.

TESTS AND RESEARCH

EGPWS

Data extracted from the EGPWS indicated that about 3 seconds prior to landing the TAWS generated a mode 1 sink rate alert. A mode 1 alert is triggered by an excessive rate of descent and provides warnings and advisories when the airplane has a large descent rate with respect to the altitude above ground level during descent and approach. If the airplane barometric descent rate becomes excessive, the aural "Sink Rate" message is heard and the amber "GND PROX" light comes on. If the descent rate becomes severe, the aural changes to "Pull Up," the red "Pull Up" indication shows, and the master warning lights illuminate.

The EGPWS provides a Mode 7 windshear warning signal when the airplane is flying into an excessive windshear condition during takeoff or approach and windshear warnings take priority over all other ground proximity warning system alerts, however, the alerts are suppressed below 50 feet radio altitude. The EGPWS receives data from the Weather Radar system in order to analyze a windshear condition and trigger an alert. No Mode 7 alert was indicated during approach in the data extracted from the EGPWS.

Wind components calculated from FDR data indicated that in the 4 seconds prior to touchdown, vertical wind transformed from a 6 feet per second (fps) updraft to a 19 fps downdraft and a 17 knot headwind just prior to touchdown changed to a 1 knot tailwind.

Weather Radar and Predictive Windshear Alerts 

The weather radar system uses Doppler shift along the radar beam to predict gusts in precipitation ahead of the airplane and requires moisture in the air in order for radar energy to be reflected. If the calculated gust exceeds a specified threshold, an alert is triggered.

The Honeywell Weather/Windshear Radar RTA-4B, serial number RTA4B-15561 was removed from the airplane and shipped to the Honeywell International engineering facility for examination. The unit was connected to an engineering test stand to query the section of the unit's non-volatile memory (NVM) to identify and download pertinent data. The examination revealed that no predictive windshear events were recorded in the NVM.

ORGANIZATIONAL AND MANAGEMENT INFORMATION

Omni Air International, Inc. was a privately owned and managed FAA part 121 certificated air carrier that conducted worldwide passenger charter operations. Information obtained on the company website indicated that Omni Air International, Inc. conducted operations using a fleet of Boeing 777-200ER, 767-300ER, and 767-200ER aircraft.

ADDITIONAL INFORMATION

The Omni Air International Flight Crew Training Manual contained guidance for pilots on landing technique. This guidance was consistent with that of the manufacturer and stated, in part, to avoid rapid control column movements during the flare and that the normal touchdown attitude should be about 4 – 6 degrees nose up with a touchdown airspeed between reference speed and 5 knots below reference speed. 

The flight crew briefed a planned reference speed of 145 knots. FDR data indicated that during the last 1000 feet of the approach descent, the autothrottle was engaged and the airspeed varied between about 162 knots and 150 knots and engine N1 varied between about 81% and 62%. The autothrottle was disconnected at about 210 feet above the ground when the N1 was about 50%. Subsequently, the N1 was gradually reduced to about 40% N1 by about 110 feet above the ground and remained there until touchdown.

Data from the FDR indicated the airplane touched down at approximately 140 knots. The pitch increased from approximately 1° just prior to the flare to the maximum pitch reached during landing of 9.5° and the maximum vertical acceleration recorded was approximately +2.5 G's.

Charts and guidance included in the manufacturers and operators flight manuals indicated that at touchdown, the pitch attitude exceeded the contact limit of the airplane. 

After two tailstrike occurrences in the B-767 fleet at Omni Air International in 2012, the Fleet Manager issued a memo drawing attention to the risk of tailstrikes and providing guidance on tailstrike avoidance. The memo included a review of information contained in the Flight Crew Training Manual and identified a slower than normal airspeed as a cause of tailstrike occurrences.

The Q4 2013 edition of Boeing's Aero Magazine included an article titled "Avoiding Tailstrikes" which included guidance on takeoff and landing procedures to avoid tailstrikes. The article identified unstabilized approach and mishandling of crosswinds as factors that increase the chance of a tailstrike. The article emphasized the need to maintain a minimum of reference speed minus 5 knots at the beginning of the landing flare to reduce the chance of tailstrike during landing.

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