NTSB recommends larger drain holes in Citation Excel tails

March 17, 2011

The U.S. NTSB recommends the FAA to issue an airworthiness directive to require that all Cessna 560XL operators comply with Cessna service letter 560XL-53-08, which asks operators to drill a drain hole in the bulkhead.

The National Transportation Safety Board (NTSB)  issued this recommendation in the light of the investigation of three incidents involving Cessna 560XL Citation Excel airplanes that experienced loss of rudder control after ice built up inside the tailcone.

Ice found in the bottom of the tailcone (photo: NTSB)

Preliminary findings indicate that water can collect inside the tailcone and then freeze around and restrict the movement of the rudder boost cables and pulleys. As long as the frozen ice impedes the cables and pulleys, the pilot may be unable to deflect the rudder, which is particularly dangerous when attempting to land in a crosswind or maneuver on the runway. Normally, a pilot would not use the rudder during cruise flight and would not detect that the rudder was frozen until just before or after landing.

Although the investigations are ongoing, the information gathered to date has raised serious concerns about the potential loss of rudder control when ice builds up inside the tailcone.

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Four recent uncontained engine failure events prompt NTSB to issue urgent safety recommendations to FAA

May 28, 2010

The National Transportation Safety Board issued two urgent safety recommendations to the Federal Aviation Administration (FAA) following four recent events in which the aircraft experienced an uncontained engine failure of its GE CF6-45/50 series engine.

The first recommendation asks that the FAA require operators of aircraft equipped with a particular model engine to immediately perform blade borescope inspections (BSI) of the high pressure turbine rotor at specific intervals until the current turbine disk can be redesigned and replaced with one that can withstand the unbalance vibration forces from the high pressure rotor. The second recommendation asks the FAA to require the engine manufacturer to immediately redesign the disk. The NTSB issued an additional recommendation for a requirement that operators perform a second type of inspection and another recommendation related to the engine manufacturer regarding the installation of the replacement disk.

All four recommendations apply to the low pressure turbine (LPT) stage 3 (S3) rotor disk in the General Electric (GE) CF6-45/50 series turbofan engines that can fail unexpectedly when excited by high-pressure (HP) rotor unbalance.
An uncontained engine event occurs when an engine failure results in fragments of rotating engine parts penetrating and exiting through the engine case. Uncontained turbine engine disk failures within an aircraft engine present a direct hazard to an airplane and its passengers because high-energy disk fragments can penetrate the cabin or fuel tanks, damage flight control surfaces, or sever flammable fluid or hydraulic lines. Engine cases are not designed to contain failed turbine disks. Instead, the risk of uncontained disk failure is mitigated by designating disks as safety-critical parts, defined as the parts of an engine whose failure is likely to present a direct hazard to the aircraft.
In its safety recommendations to the FAA, the NTSB cited four foreign accidents, which the NTSB is either investigating or participating in an investigation led by another nation, in which the aircraft experienced an uncontained engine failure of its GE CF6-45/50 series engine.

The date, location, and circumstances of these four events (none had injuries or fatalities) are as follows:

On July 4, 2008, a Saudi Arabian Airlines (Saudia) Boeing 747-300 experienced an engine failure during initial climb after takeoff from Jeddah, Kingdom of Saudi Arabia. This investigation has been delegated to the NTSB.

On March 26, 2009, an Arrow Cargo McDonnell Douglas DC-10F, about 30 minutes after takeoff from Manaus, Brazil, experienced loss of oil pressure in one engine. The pilots shut down the engine and diverted to Medellin, Columbia. This investigation has been delegated to the NTSB.

On December 17, 2009, a Jett8 Cargo Boeing 747-200F airplane was passing through 7,000 feet above ground level (agl) when the flight crewmembers heard a muffled explosion and immediately applied left rudder. With one engine losing oil pressure, the airplane returned to land at Changi, Singapore. The NTSB is participating in the investigation that is being led by the Air Accident Investigation Bureau of Singapore.

On April 10, 2010, an ACT Cargo Airbus A300B4 experienced an engine failure while accelerating for takeoff at Manama, Bahrain. The crew declared an emergency, rejected the takeoff, activated the fire suppression system, and evacuated the airplane. The NTSB is participating in the investigation that is being led by the Bahrain Ministry of Transportation – Civil Aviation.
The four recommendations to the FAA are as follows:
1. Immediately require operators of CF6-45/50-powered airplanes to perform high pressure turbine rotor blade borescope inspections every 15 flight cycles until the low pressure turbine stage 3 disk is replaced with a redesigned disk that can withstand the unbalance vibration forces from the high pressure rotor. (Urgent)

2. Require operators of CF6-45/50-powered airplanes to perform fluorescent penetrant inspections of CF6-45- 50- low pressure turbine stage 3 disks at every engine shop visit until the low pressure turbine stage 3 disk is replaced with a redesigned disk that can withstand the unbalance vibration forces from the high pressure rotor.

3. Immediately require General Electric Company to redesign the CF6-45/50 low pressure turbine stage 3 disk so that it will not fail when exposed to high pressure rotor unbalance forces. (Urgent)

4. Once General Electric Company has redesigned the CF6- 45/50 low pressure turbine (LPT) stage 3 disk in accordance with Safety Recommendation [3], require all operators of CF6-45/50-powered airplanes to install the newly designed LPT S3 at the next maintenance opportunity.


Airport safety recommendations after Indonesian B737 runway excursion accident

May 18, 2010

Wreckage of the Boeing 737 after it came to rest in an area of shallow muddy water surrounded by mangrove vegetation. Photo: NTSC

The Indonesian National Transportation Safety Committee (NTSC) issued their preliminary report regarding the runway excursion accident involving a Boeing 737. Seven safety recommendations were issued addressing various aspects of airport safety.

On April 13, 2010 a Boeing 737-322 passenger plane, registered PK-MDE, sustained substantial damage in a runway excursion accident at Manokwari-Rendani Airport (MKW/WASR), Indonesia. All 103 passengers and seven crew members survived but ten sustained serious injuries.
Merpati Flight MNA836 operated on a scheduled flight from Sorong-Dominique Edward Osok Airport (SOQ/WAXX). Departure was delayed for almost three hours due to heavy rain over Manokwari.
On approach Rendani Radio informed the crew that the weather was continuous slight rain, visibility 3 kilometers, cloud overcast with cumulus-stratocumulus at 1,400 feet, temperature 24 degrees Celsius, QNH 1012 hectopascals.
At 10:54 the crew reported that they were on final for runway 35. The controller informed them that the wind was calm, runway condition was wet and clear.
The crew read back the wind condition and that the runway was clear, but did not mention the wet runway condition.
The aircraft was observed to make a normal touchdown on the runway, about 120 meters from the approach end of runway 35. Witnesses on the ground and on board reported that engine reverser sound was not heard during landing roll.
During the landing roll, the aircraft veered to the left about 140 meters from the end of runway 35, then overran the departure end of runway 35. It came to a stop 205 meters beyond the end of the runway in a narrow river; the Rendani River.
The airport rescue and fire fighting unit was immediately deployed to assist the post-crash evacuation. Due to the steep terrain 155 meters from the end of runway 35, the rescuers had to turn back and use the airport’s main road to reach the aircraft. The accident site was in an area of shallow muddy water surrounded by mangrove vegetation.

Seven safety recommendations were issued:

1) The Directorate General Civil of Aviation (DGCA) should ensure that Merpati Nusantara Airlines Operational Specifications and other technical and operational safety requirements are met.

2) DGCA should urgently review the Rendani Airport, Manokwari runway complex, to ensure that the runway end safety areas (RESA) meet the dimension Standards prescribed in ICAO Annex 14.

3) DGCA should urgently review all airports involving Part 121 and 135 operations, to ensure that the runway end safety areas (RESA) meet the dimension Standards prescribed in ICAO Annex 14.

4) DGCA should urgently ensure that Indonesian airports equipped with visual approach slope guidance systems, maintain the equipment to a serviceable standard.

5) DGCA should review the procedures and equipment used by airport Rescue and Fire Fighting Services to ensure that they a) meet the minimum requirements, including timeliness, specified in ICAO Annex 14; and b) meet the requirements to cover the area up to 5 NM (8 Km) from the airport perimeter.

6) Merpati should review its technical and operational safety requirements to ensure they are implemented.

7) Merpati should review equipment used by airport Rescue and Fire Fighting Services at airports in its network, to ensure that they meet the minimum requirements for Boeing 737 aircraft.


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