NTSB Factual Report

HISTORY OF FLIGHT

On October 28, 2016, about 1751 eastern daylight time, FedEx Express (FedEx) flight 910, a McDonnell Douglas MD-10-10F, N370FE, experienced a left main landing gear (MLG) collapse after landing on runway 10L at Fort Lauderdale–Hollywood International Airport (KFLL), Fort Lauderdale, Florida, and the left wing subsequently caught fire. The airplane came to rest off the left side of the runway. The two flight crewmembers evacuated the airplane. The captain reported a minor cut and abrasions from the evacuation, and the first officer was not injured. The airplane sustained substantial damage. The cargo flight was operating on an instrument flight plan under the provisions of Title 14 Code of Federal Regulation (CFR) Part 121 and originated at Memphis International Airport (KMEM), Memphis, Tennessee.

The first officer was the pilot flying, and the captain was the pilot monitoring. Both flight crewmembers stated in postaccident interviews that the departure from MEM and the en route portion of the flight were normal. About 1745, air traffic control (ATC) cleared the flight for final approach to the instrument landing system (ILS) approach to runway 10L at KFLL. Recorder data indicate that the first officer set the flaps at 35º about 1746 when the airplane was 3,000 ft above ground level (agl). The first officer disconnected the autopilot about 1749 when the airplane was 1,000 ft agl. Both flight crewmembers reported that the approach was stable at 500 ft agl. At 200 ft agl, the first officer began making airspeed corrections to compensate for the crosswind. About 1750, the first officer disconnected the autothrottles, as briefed, when the airplane was at 100 ft agl.

At 50 ft agl, the first officer initiated the flare. The left MLG touched down about 1750:31 in the touchdown zone and left of the runway centerline. The first officer deployed the spoilers at 1750:34, and the nose gear touched down 3 seconds later. The thrust reversers were deployed at 1750:40. According to cockpit voice recorder (CVR) data, the captain instructed the first officer to begin braking about 1750:39 (the airplane was not equipped with autobrakes). FDR data indicate an increase in brake pedal position angle and increase in longitudinal deceleration (indicating braking) about 1750:41. In postaccident interviews, the flight crewmembers reported hearing a "bang" as the first officer applied the brakes, and the airplane yawed to the left. About this time, the CVR recorded the sound of multiple thuds, consistent with the sound of a gear collapse.

About 1750:48, the captain stated, "I have the airplane," and the first officer replied, "you got the airplane." The captain applied full right rudder without effect while the first officer continued braking. About 1750:53, the captain instructed the first officer to call and inform the tower about the emergency.

An airport video of the landing showed that the No. 1 engine was initially supporting the airplane after the left MLG collapse when a fire began near the left-wing tip. The airplane eventually stopped off the left side of runway 10L, about 30º to 40º off the runway heading. About 1751, the flight crew began executing the evacuation checklist. The pilots reported that, as they were about to evacuate, they heard an explosion. The airport video showed a fireball erupted at the No. 1 engine. The captain attempted to discharge a fire bottle in the No. 1 engine, but it didn't discharge. They evacuated the airplane through the right cockpit window.

PERSONNEL INFORMATION

The two crewmembers had flown together previously and reported having a good rapport. The departure from MEM was the first leg of the most recent flight pairing.

The Captain

The captain, age 55, was hired as a flight engineer by FedEx in 2000. At the company, he worked in the Boeing 727 as a flight engineer, a first officer, and a captain, as well as a captain on the MD-11. He had a total flight time of about 10,000 hours (he was uncertain about his time as pilot-in-command) and estimated about 1,500 hours in the MD-11. The captain held a multiengine airline transport pilot certificate, with type ratings in the LR-Jet, Boeing 727, and MD-11. The captain held a Federal Aviation Administration (FAA) first-class airman medical certificate dated June 6, 2016, with a limitation that he "must have glasses available for near vision."

The First Officer

The first officer, age 47, was hired as a flight instructor by FedEx in 2004. In 2007, he became a flight engineer in the Boeing 727 and became a first officer in the MD-11 in 2012. He estimated a total flight time of 6,000 to 6,300 hours, with about 4,000 hours as pilot-in-command. He estimated a total time of about 400 to 500 hours in the MD-11, with no time as pilot-in-command. The first officer held a multiengine airline transport pilot certificate, with a type rating in the MD-11. The first officer held an FAA first-class airman medical certificate dated September 6, 2016, with no limitations.

AIRPLANE INFORMATION

The airplane, a McDonnell Douglas MD-10-10F, serial number 46608, registration N370FE, was manufactured in 1972 and had an airframe total time of 84,589 total flight hours with 35,606 total flight cycles at the time of the accident. FedEx purchased the airplane on August 21, 1997. The airplane was converted from a DC10-10 to a DC10-10F on July 3, 1999; it was converted to an MD-10-10F on November 2, 2003, when a transport-category standard airworthiness certificate was also issued. It was powered by three General Electric model CF6-6D turbo-fan engines. The airplane's last "C" check was on September 21, 2016. It's last inspection as October 25, 2016, when a service check, an "A" check, and a "B check" were completed.

Left Main Landing Gear

The most recent overhaul of the left MLG occurred February 28, 2008, by Hawker Pacific Aerospace (HPA) Repair Station No. RJ3R817L in Sun Valley, California. It was installed on the accident airplane March 31, 2008. Aircraft time at installation was 74,340.02 total flight hours and 29,953 total cycles. Time since installation was 10,249.03 flight hours, 5,653 cycles, and 3,133 days (8.58 years). At the time of the accident, the MLG overhaul limit at FedEx was 9 years or 30,000 flight hours, whichever occurs first; the left MLG's time remaining until the next overhaul was 152 days (most restrictive). The Boeing maintenance planning document recommends the restoration (overhaul) of the MLG assembly every 8 years or 7,500 flight cycles, whichever occurs first. A FedEx representative indicated that the company adopted the 9-year MLG overhaul limit used by the previous owner/operator of the first DC10s purchased by FedEx.

The most recent service of the MLG full shock strut was performed at the airplane's last "C" check in September 2016, in Mobile, Alabama (this work included draining and replacing the strut fluid and nitrogen charge; it does not include a requirement to do a borescope inspection of the air fill valve bore).

In addition, aircraft log writeups revealed a pilot report dated February 6, 2014, indicated a hard landing that occurred at Newark Liberty International Airport, Newark, New Jersey. Maintenance personnel downloaded and reviewed FDR data and performed structural inspections in accordance with manufacturer specifications. No defects were noted during the inspections, and no additional work was required.

Maintenance History of the Left MLG Outer Cylinder

Of the 3 airworthiness directives and 14 service bulletins (SB) accomplished during the left MLG's last overhaul, the work associated with Alert Service Bulletin DC10-32A259 was identified for further examination based on findings in the NTSB's investigation. Maintenance records indicate that no stray nickel or chrome was found during the initial inspection of the air filler valve bore, but corrosion was found and removed per ASB instructions. The MLG cylinder was then brush cadmium plated per the CMM (see Additional Information). The overhaul was completed on February 28, 2008.

All dimensions related to the fill valve bore rework were documented in HPA work cards indicating the air filler valve bore was oversized within manufacturer limits, and all recorded dimensions were within manufacturer limits with one exception. The ASB and CMM state that the radius of the air fill valve bore at both the inner diameter wall and thread junction should be maintained at 0.015 to 0.030 inch during rework and that findings be recorded. After rework, the thread junction radius was recorded as 0.030 inch and the inner diameter wall was recorded as 0.090 inch. No additional records were found that addressed the exception. When asked about this exception, a Boeing representative indicated that this type of discrepancy had been brought to the manufacturer's attention previously and that larger radius findings had been approved for continued service.

METEOROLOGICAL INFORMATION

About an hour before the accident, at 1653, the KFLL METAR reported wind from 50° at 15 knots gusting to 25 knots, 10 miles visibility, few clouds at 2,400 ft agl, scattered clouds at 3,300 ft agl, broken ceiling at 4,100 ft agl, overcast clouds at 25,000 ft agl, temperature 26°C, dewpoint 20C, and an altimeter setting of 29.99 inches of mercury.

At 1753, about 2 minutes after the accident, the KFLL METAR reported wind from 050° at 15 knots gusting to 24 knots, 10 miles visibility, few clouds at 2,600 ft agl, broken ceiling at 5,000 ft agl, overcast clouds at 25,000 ft agl, temperature 26°C, dewpoint 21°C, and an altimeter setting of 29.98 inches of mercury. A peak wind speed had been recorded at 1732 of 060 degrees at 26 knots.

AIRPORT INFORMATION

KFLL is located about 3 miles southwest of downtown Fort Lauderdale. The airport has two parallel east/west runways (10L/28R and 10R/28L). The airport elevation is 9 ft above mean sea level. Runway 10L/28R is 9,000 ft long and 150 ft wide and is constructed of grooved asphalt. It is equipped with an instrument landing system approach and a medium intensity approach lighting system with runway alignment indicator (MALSR).

FLIGHT RECORDERS

The accident airplane was equipped with a Honeywell model 980-4700-042, 256-word solid-state FDR, serial number 10591. The recorder was in good condition and the data were extracted normally. The FDR recording contained about 27.2 hours of data. The event flight was the last flight of the recording and its duration was about 2 hours.

The accident airplane was equipped with a General Electric (GE) combination cockpit voice flight data recorder (CVFDR), model number 175497-01-01, serial number 0000061. Four channels are recorded: one channel for each flight crew, one channel for a cockpit observer, and one channel for the cockpit area microphone. Good-to-excellent quality audio information was extracted from the recorder normally (the observer channel, number 2, didn't contain any audio information and wasn't expected to since there wasn't an observer pilot on the flight). A cockpit voice recorder group was convened at the NTSB audio laboratory and a partial transcript for the 2-hour digital recording was produced.

WRECKAGE AND IMPACT INFORMATION

The airplane came to rest off the left side of runway 10L near the A4 taxiway. The outer cylinder of the left MLG was fractured midway through the air filler valve bore on the aft side. The outer cylinder of the left MLG shock strut fractured around its entire circumference; the upper portion of the cylinder remained intact and attached to the airplane at the forward and aft trunnion lugs (figure 1 shows a diagram of an MD-10-10F MLG and figure 2 shows the upper portion of the accident MLG). No anomalies were noted with the trunnion lugs or trunnion bolt attachment points.

The inboard side lugs and bolt and nut for the retract actuator attach points and the fixed door attach points remained intact. On the aft side of the lower section of the fractured gear, about half of the upper charging bore was visible (see figure 3). On-scene examination identified features consistent with fatigue on the fracture surface of the outer cylinder in the area of the air filler valve bore (see Tests and Research for more information).

The lower segment of the landing gear was folded aft into the left side inboard flap. The lower portion of the gear remained attached to the MLG side brace assembly. The left MLG truck beam remained attached to the lower portion of the cylinder and shock strut at the pivot pin. The truck beam exhibited a crack running aft from the No. 1 wheel position axle to a 3-inch-long by 2-inch-wide hole on the top side near the pivot area (see MLG diagram in figure 3).

Three pieces of the left MLG outer cylinder were found on the runway. One piece measured about 12 to 14 inches long by about 30 inches in circumference. Two smaller portions, about 2 by 2 inches and 3 by 3 inches, from the upper charging bore and boss were also found on the runway. The upper charging bore fill valve was not found. These pieces, along with the remainder of the left MLG cylinder were sent to the NTSB Materials Laboratory for examination. The fracture surface of the 3-by-3-inch section had features consistent with fatigue in the area of the upper charging bore (see Tests and Research for more information).

Several of the internal components of the left MLG shock strut were recovered from the runway, including the upper chamber, the orifice assembly, the upper bearing, the metering pin (fractured), and the upper bearing carrier (2 halves).

The left wing sustained fire damage that extended from inboard of the No. 1 engine pylon outboard to the left wingtip and chordwise from the leading-edge wing spars to the aft trailing edge wing spars. The left wing trailing edge upper and lower closeout panels, inboard and outboard flaps, and ailerons sustained damage from the impact and fire. Slats 2 and 3 surrounding the No. 1 engine and pylon sustained fire damage. Slats 4 through 8 had impact damage. The bottom of the left-wing fuel tank sustained structural damage during the accident sequence.

The bottom of the No. 1 engine had two large scraped areas. The forward scrape was along the bottom of the cowling doors, and the second scrape extended aft from the aft edge of the thrust reverser blocker vanes. The No. 1 pylon fuel tube was found torn and partially consumed by fire, and the firewall shutoff valve was found in the closed position. The No. 1 pylon sustained both fire damage and structural damage due to impact.

The pilots reported hearing an explosion as they were preparing to evacuate and a fireball was captured by an airport surveillance camera after the airplane came to a stop. The recording shows a large portion of debris above the fireball and at more than twice the height of the 75-ft-tall airplane tail. A large portion of the heavy structure of the left main fuel tank upper skin was found near the left-wing tip, 25 ft in span by 8 ft in cord, as well as smaller fragments. Burns and melting damage to the forward and lower exterior surfaces of the left main fuel tank were found near where the fuel supply tube had broken in the engine pylon.

TESTS AND RESEARCH

Materials Laboratory

The left MLG cylinder and fragments found on the runway were examined at the NTSB Materials Laboratory. A small thumbnail crack was observed on the 3-by-3-inch fragment at the radius between the cylinder inner diameter surface and the valve bore surface that was consistent with a pre-existing crack before the complete fracture of the MLG. Most of the fracture surface area had been damaged by smearing, consistent with post-fracture impact damage. Surface contamination, such as rust and dirt, were also present. A small area next to the radius exhibited features (such as crack arrest marks) consistent with progressive crack growth. The progressive crack growth was found to be fatigue cracking, as exhibited by the fatigue striations found on microscopic examination of the thumbnail crack.

Metallurgical examination of the main fracture region of the left MLG cylinder found almost all of the fracture surfaces exhibited a dull luster with a rough surf

NTSB Probable Cause

The failure of the left main landing gear (MLG) due to fatigue cracking that initiated at a corrosion pit. The pit formed in the absence of a required protective cadmium coating the cause of which could not be determined from available evidence. Contributing to the failure of the left MLG was the operator's overhaul limit, which exceeded that recommended by the airplane manufacturer without sufficient data and analysis to ensure crack detection before it progressed to failure.