Unexpected Contamination

The following information provides an awareness of problems that might be avoided in the future. The information is based on final reports by official investigative authorities on aircraft accidents and incidents.

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JETS

Late Touchdown Faulted

Boeing 737-800. No damage. No injuries.

The investigation of a runway-overrun incident has prompted the U.K. Air Accidents Investigation Branch (AAIB) to recommend the establishment of a single definition of what constitutes a contaminated runway and the development of an accurate and timely method of measuring the depth of runway contaminants, so that pilots can obtain the information they need to determine required landing distances.

A significant difference between the reported and the actual surface condition of the runway at Newcastle (England) Airport the night of Nov. 25, 2010, was a likely factor that led to an encounter with braking action that was less than the flight crew anticipated and to the 737 coming to a stop with its nosewheel 3 m (10 ft) beyond the end of the runway, said the AAIB in its final report on the incident.

Other factors included “touchdown of the aircraft beyond the normal touchdown zone and selection of idle reverse thrust before the aircraft was at taxi speed,” the report said.

The 737 was inbound from Lanzarote, Canary Islands. Snow showers had been forecast for Newcastle, so the flight crew had decided to carry an additional 1,100 kg (2,425 lb) of fuel for a possible diversion to Edinburgh, Scotland.

The crew conducted a landing performance calculation with the “C-Land” application for a laptop computer, which showed that “at their expected landing weight, they would be able to accept a wet runway and a slight tailwind” at Newcastle, which has a single 2,329-m (7,641-ft) runway, the report said. “They also decided that if the runway had more than 3 mm [0.12 in] of contaminant, this would mean that it was contaminated, which was not acceptable for their operation.”

However, the report noted that guidance on what constitutes a contaminated runway varies among U.K. aviation publications. The crew’s conception that a runway meets their company’s designation as contaminated when it has more than 3 mm of slush or wet snow was in keeping with guidance provided by U.K. Civil Aviation Authority (CAA) Aeronautical Information Circular 86/2007, Risks and Factors Associated With Operations on Runways Affected by Snow, Slush or Water. It contradicted the definition contained in Civil Aviation Publication 683, The Assessment of Runway Surface Friction Characteristics, which “considers a runway as contaminated when any depth of slush or wet snow is present,” the report said.

“The CAA stated that material contained across CAA documentation relating to contaminated runway operations is targeted at different audiences, and, therefore, there are necessary differences in style and content,” the report said. “However, the inconsistencies concerning the definition of a contaminated runway surface … could cause pilots to assess incorrectly the contamination state of a runway.”

During the flight from Lanzarote, the pilots received several reports indicating that the weather conditions at Newcastle were changing rapidly. However, runway condition was consistently reported as wet. “Using the C-Land application, the pilots calculated that the landing distance required for a wet runway was approximately 300 m [984 ft] less than the landing distance available,” the report said.

The crew planned to conduct the instrument landing system (ILS) approach to Runway 07. While briefing the approach, the copilot, the pilot flying, said that he would use full flaps and the highest autobrake setting below maximum, and apply full reverse thrust after touchdown. “The crew briefly discussed the possibility of using maximum autobrake for the landing but decided this was unnecessary,” the report said.

A weather report issued while the 737 was on the ILS approach indicated that surface winds were from 310 degrees at 13 kt, visibility was 4,500 m (2.8 mi) in wet snow, and there were scattered clouds at 400 ft and a broken ceiling at 800 ft. The crew of a preceding aircraft reported “medium to good” braking action on the runway.

However, the 737 crew initiated a missed approach when the airport traffic controller relayed a runway inspection report indicating that there was 3 to 4 mm (0.16 in) of snow on the runway. They entered a holding pattern, “intending to hold there until either the runway had been cleared sufficiently for them to make a second approach or it became necessary to divert to Edinburgh,” the report said.

About 10 minutes later, the controller told the crew that sweeper vehicles had completed one pass over the runway and that 2 mm (0.08 in) of wet snow remained on the surface. “Judging that the runway was no longer contaminated, the pilots updated the landing data for a wet runway … and carried out a second approach,” the report said.

The 737 touched down at 140 kt about 450 m (1,476 ft) from the approach threshold — or about 150 m (492 ft) from the normal touchdown point, the report said. The spoilers deployed automatically, the autobrakes activated, and reverse thrust was applied. Groundspeed was about 97 kt when the copilot disengaged the autobrakes and reduced reverse thrust to idle.

“After the reduction in reverse thrust, there was a notable decrease in the aircraft deceleration,” the report said. “Application of full manual braking appeared not to change the deceleration, [which was] not consistent with the ‘good’ braking action anticipated by the crew.”

The commander assumed control as the 737 neared the end of the runway at a groundspeed of about 50 kt. With both pilots applying manual wheel braking, the aircraft came to a stop near the runway centerline but with its nosewheel beyond the runway end lights. None of the 189 passengers and eight crewmembers was injured, and there was no damage. The pilots shut down the engines, and the passengers and cabin crewmembers were transported to the terminal by airport vehicles before the aircraft was towed to the ramp.

“Both pilots independently walked on the runway back towards the Runway 25 displaced threshold and assessed the surface as very icy,” the report said.

In addition to recommending elimination of inconsistencies among the definitions of a contaminated runway, the report discussed research currently being conducted by the CAA, the European Aviation Safety Agency and the U.S. Federal Aviation Administration on accurate and timely methods of measuring runway contamination and providing the information to pilots for use in calculating required landing distances (see “Friction-Reporting Caveats,” p. 13).

Aileron Servo Bracket Fails

Airbus A330-301. Minor damage. No injuries.

Because of a large cloud of ash streaming south from a volcano in Iceland, the flight crew planned to take a more northerly route than normal for the scheduled flight with 227 passengers and 11 crewmembers from Dublin, Ireland, to Chicago on the afternoon of May 11, 2010.

“Due to the funneling of aircraft tracks in the Icelandic area arising from the presence of the ash cloud to the southwest, there was considerable congestion in the airspace over Iceland,” said the report by the Irish Air Accident Investigation Unit (AAIU).

The A330 was cruising at Flight Level (FL) 330 (approximately 33,000 ft) over Iceland when it encountered moderate turbulence, which the crew believed was caused by the wake of another aircraft. “The turbulence resulted in some aircraft roll and yaw,” the report said. “The autopilot, which remained engaged during the turbulence encounter, quickly returned the aircraft to level flight.”

Shortly thereafter, air traffic control cleared the crew to climb to FL 380. During the climb, the crew noticed that the vertical velocity was lower than expected and that fuel consumption was higher than expected. They found that the anomalies were being caused by the abnormal deflection of all four ailerons. The electronic centralized aircraft monitor (ECAM) showed that the inboard aileron on the right wing was deflected 15 degrees up and that the outboard aileron on the right wing and both ailerons on the left wing were deflected about 10 degrees down.

“The flight crew for this particular flight consisted of three pilots, so the captain was able to leave the flight deck and go to the cabin, where he obtained visual confirmation that the physical configuration of the ailerons corresponded with the indications on the ECAM,” the report said.

No warnings or cautions were displayed on the ECAM. While troubleshooting the problem in consultation with company maintenance personnel, the flight crew found no difficulty in maneuvering the A330 with the autopilot either engaged or disengaged. They decided to continue the flight to Chicago O’Hare International Airport, where the aircraft was landed without further incident.

Investigators determined that while the autopilot was correcting the turbulence-induced roll over Iceland, the outer mounting bracket on a servo controller for the right inboard aileron had fractured, causing the aileron initially to oscillate and then to settle in the upward deflection. The corresponding bracket in the left wing also was found cracked.

Examination of the broken bracket by Airbus revealed that fatigue cracking had originated from a 50-micron pit that had formed during manufacture. Previous incidents involving failed or cracked servo controller brackets on A330s and A340s had prompted a service bulletin to be issued in 2009, calling for eddy current inspections. Although the incident aircraft had been inspected according to the service bulletin, AAIU investigators determined that the testing probe used during the inspection had provided false indications that the brackets were sound.

Driver’s Foot Slips Off Brake

Boeing 737-700. Substantial damage. No injuries.

The737 was parked at a gate at Fort Lauderdale/Hollywood (Florida, U.S.) International Airport, and about half of the passengers had deplaned the afternoon of Oct. 29, 2010, when a driver began moving a lavatory-service vehicle backward toward the airplane.

“A guide man signaled the driver to stop the vehicle for a brake check, which he did,” the U.S. National Transportation Safety Board (NTSB) report said. “The guide man then signaled the driver to resume reversing the vehicle and subsequently signaled the driver to stop in the service position, located about 3 ft [1 m] from the airplane’s fuselage.”

The driver stopped the vehicle but did not place the transmission in the park position; his foot then slipped off the brake pedal and onto the accelerator. The vehicle backed into the airplane, tearing a 12- by 6-in (30- by 15-cm) hole in the fuselage and damaging some stringers.

The report said that the driver, who was “twisted around” in his seat to see the guide man when the accident occurred, was not wearing required work boots and that a rubber cover was missing from the brake pedal.

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‘Beyond Their Performance Limit’

Dornier 328-100. Substantial damage. Five minor injuries.

Investigators concluded that among the factors leading to a runway overrun at Mannheim City Airfield on March 19, 2008, was that the flight crew deviated from standard operating procedures, “reached their performance limit and, at the end, went beyond it.” Other factors included the crew’s “non-initiation of a balked landing” and their inability to deploy the thrust reversers after a bounced landing and touchdown near the end of the runway, according to the German Federal Bureau of Aircraft Accident Investigation (BFU).

The accident occurred during a scheduled evening flight with 24 passengers and three crewmembers from Berlin. The pilots, who had not flown together previously before completing a flight from Mannheim to Berlin earlier that day, were returning to Mannheim with the first officer flying from the right seat, said the final report, issued by the BFU in August.

The airport had surface winds from 330 degrees at 12 kt, gusting to 18 kt, 4,000 m (2 1/2 mi) visibility in snow showers and a broken ceiling at 1,400 ft. The 1,066-m (3,498-ft) runway was clear and dry.

Before initiating the localizer/distance-measuring equipment approach to Runway 27, the first officer expressed reservations about conducting the landing. The pilot-in-command (PIC), who was far more experienced and much older than the first officer, replied, “It will all work out.”

The report indicated that the approach was not stabilized and neither pilot called for a go-around. The first officer did not respond when the PIC told him to reduce power to flight idle after the airplane crossed the runway threshold. The Dornier floated about 10 ft above the runway after the first officer initiated a flare and was about 200 m (656 ft) beyond the runway threshold when he abruptly transferred control to the PIC, which was “not a reaction appropriate to the situation,” the report said.

The aircraft touched down beyond the midpoint of the runway, bounced and touched down again about 480 m (1,575 ft) from the end. The power levers were still forward of the flight idle position, and the PIC was unable to engage the thrust-reverse system.

The report said that recorded flight data showed no significant deceleration. The PIC engaged the parking brake, and the locked main wheels left tire skid marks for about 150 m (492 ft) before the Dornier overran the runway at about 30 kt. The left main landing gear collapsed, and the nose and left wing struck an embankment before the aircraft came to a stop.

Distraction Leads to Stall

Beech King Air 100. Substantial damage. One fatality, four serious injuries, five minor injuries.

The departure for a scheduled flight from Edmonton to Kirby Lake, both in Alberta, Canada, the morning of Oct. 25, 2010, was delayed about one hour because the weather conditions were below minimums at the destination. When the flight got under way, Kirby Lake had surface winds from 170 degrees at 8 kt, gusting to 16 kt, 4 mi (6 km) visibility in light snow and a 600-ft overcast.

“During the descent and approach to Kirby Lake, the crew engaged in nonessential conversation that was not related to the operation of the aircraft,” said the report by the Transportation Safety Board of Canada.

The crew conducted the area navigation approach to Runway 08, with the first officer as the pilot flying (PF). His workload was affected by the need to include the captain’s horizontal situation indicator (HSI) in his instrument scan because global positioning system track information was fed only to the captain’s HSI. The King Air encountered icing conditions, and the crew cycled the deicing boots six times during the approach.

Required altitude callouts were not made, and the captain saw the runway after the aircraft descended below the published minimum descent altitude. “The PF was not able to identify the runway,” the report said. “Throughout the remainder of the approach, both pilots were predominantly looking outside the aircraft.”

The captain pointed out a road and a radio tower, and their locations in relationship to the airport. However, the first officer did not see the runway until the King Air was less than 1 nm (2 km) from the approach threshold. The aircraft stalled shortly thereafter, with no aural warning. “Maximum power was required, but recovery was not achieved prior to the aircraft hitting the ground” 174 ft (53 m) from the runway, the report said.

The captain was killed, three passengers and the first officer were seriously injured, and the other five passengers sustained minor injuries.

Tail Strike on No-Flap Landing

Bombardier Q400. Minor damage. No injuries.

During a nonprecision approach to Southampton (England) Airport in icing conditions the evening of Nov. 30, 2010, the “FLAP POWER” caution light illuminated when the flight crew attempted to extend the flaps to the approach position.

“The crew calculated that the runway at Southampton Airport was not long enough for a flap zero approach in icing conditions and decided to carry out an ILS approach to Runway 08 at Bournemouth Airport,” the AAIB report said.

The approach was stabilized, and the commander disengaged the autopilot at 1,000 ft, in accordance with the emergency checklist (ECL) for a no-flap landing. As he reduced power while nearing the runway, he perceived a high rate of descent and increased the aircraft’s pitch attitude. The copilot called, “Pitch 8 degrees, don’t pitch any more.” As the Q400 touched down, the “TOUCHED RUNWAY” caution light illuminated.

The crew taxied to the stand, where the 69 passengers disembarked normally. Inspection of the aircraft revealed that the frangible touch-runway-detection switch was broken.

“The commander commented that, although he was aware of the ECL requirement to avoid pitch attitudes in excess of 6 degrees at touchdown, he found the temptation to flare the aircraft to reduce the rate of descent overwhelming,” the report said. “He also thought that the advice in the ECL to gradually reduce power to achieve flight idle at touchdown might have contributed to the aircraft’s high rate of descent.”

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Beech C55 Baron. Destroyed. Four serious injuries.

Before departing from Wilmington, Delaware, U.S., for a flight to Buffalo, New York, the afternoon of Nov. 17, 2011, the pilot requested that both main fuel tanks be topped off. However, investigators determined that the left main tank likely was only partially filled.

The pilot told investigators that he was distracted by passengers during his preflight inspection of the Baron and did not visually check the left main tank. The fuel gauge for that tank was known to be inaccurate, according to the NTSB report.

The pilot said that during cruise, he used the auxiliary tanks until they were “empty.” When he repositioned the fuel selectors to the main tanks, the left engine lost power. The pilot then attempted to configure the fuel system to crossfeed fuel from the right main tank so that he could restart the left engine. However, he did not configure the system properly, and the right engine lost power due to fuel starvation. Further attempts to start the engines were unsuccessful.

During the forced landing, the airplane crashed into a garage in Ulysses, Pennsylvania. The pilot and his three passengers were able to exit the Baron before it was consumed by fire.

Turbulence Triggers Breakup

Cessna M337B Skymaster. Destroyed. Three fatalities.

The pilot and two crewmembers were conducting a public use flight, providing aerial support for a military training exercise near MacDill Air Force Base Auxiliary Field in Avon Park, Florida, U.S., the night of Nov. 17, 2010. Forecast weather conditions had been covered during the mission briefing, but there was no indication that hazardous weather would be encountered in the military operations area, according to the NTSB report.

However, unexpected frontal movement caused weather conditions to deteriorate rapidly during the mission, with the formation of cumulus congestus clouds, the report said. The pilot decided to discontinue the flight and return to MacDill.

The Skymaster, which was not equipped with a weather radar system, entered an area of intense rain showers and severe turbulence on approach to the base. “The right wing separated in flight, and the airplane crashed inverted in a farm pasture,” the report said.

Collision in a Mountain Pass

Piper Chieftain, Cessna U206. Substantial damage. No injuries.

The Chieftain was eastbound on a visual flight rules charter flight with eight passengers from Kokhanok, Alaska, U.S., to Anchorage the afternoon of July 10, 2011. The float-equipped Cessna was westbound on a private flight with three passengers from Anchorage to Brooks Camp.

Visual meteorological conditions prevailed when the airplanes entered the opposite ends of Lake Clark Pass, about 37 nm (69 km) northeast of Port Alsworth. At an elevation of about 1,000 ft, the pass is in a river valley about 0.5 nm (0.9 km) wide and flanked by 5,000-ft mountains.

The NTSB report said that the Cessna pilot was broadcasting his position on a common traffic advisory frequency, but the Chieftain pilot was not monitoring the frequency. Neither pilot saw the other airplane or took evasive action before the top of the Chieftain’s vertical stabilizer struck the forward float spreader bar on the U206.

The collision, which occurred at 2,300 ft, caused minor damage to the Cessna’s left float and separation of the upper 18 in (46 cm) of the Chieftain’s vertical stabilizer. However, “the rudder remained attached and functional,” the report said. “Both airplanes landed safely after the collision.”

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Simulation Leads to Control Loss

Eurocopter AS350-BA. Substantial damage. Two serious injuries.

A commercial pilot was receiving instruction in night vision goggle (NVG) operations the evening of Nov. 4, 2009, when the flight instructor initiated a simulated hydraulic failure while on the downwind leg to land at Globe, Arizona, U.S.

The instructor said that the pilot did not properly adjust the trim or maintain sufficient airspeed, which decreased to about 20 kt, and the low-rotor-speed horn sounded. Both pilots were attempting to arrest the subsequent uncontrolled descent when the helicopter struck the ground, the NTSB report said.

“The pilot reported that the last time he had performed a simulated hydraulic failure was almost one year before the accident and that he had never performed such a procedure or had one demonstrated while operating with NVGs,” the report said.

Control Inputs Cause Mast Bumping

Bell 206B JetRanger. Destroyed. One fatality.

During a traffic-observation flight the morning of Oct. 15, 2010, the pilot told the two policemen aboard the helicopter that they would not be able to patrol as long as usual because he needed to obtain fuel. The pilot subsequently returned to the police department helipad in Arnold, Missouri, U.S., deplaned the passengers and departed to refuel in St. Louis.

About 20 minutes later, the engine flamed out due to fuel exhaustion, and the pilot abruptly pushed the cyclic control forward while attempting to initiate autorotative flight. “Pushing the cyclic forward abruptly is contrary to the appropriate actions for entering an autorotation, which are lowering the collective pitch control to the full-down position, adding anti-torque pedal as needed to maintain heading and applying cyclic as needed to maintain proper airspeed,” the NTSB report said.

The improper control inputs caused the main rotor hub to contact the rotor mast, a phenomenon called mast bumping. The main rotor separated, and the helicopter struck terrain near Clarkson Valley, Missouri.

“Review of the pilot’s medical records indicated that he had a history of depression, anxiety and obstructive sleep apnea,” the report said. “Each of these conditions had been documented and treated since 2007, and none were reported to the Federal Aviation Administration on the pilot’s airman medical applications.”

Toxicological testing revealed a high level of venlafaxine, an anti-depressant, in the pilot’s bloodstream, which likely had caused dizziness and impaired the pilot’s performance, the report said.