SPECIAL AIRWORTHINESS INFORMATION BULLETIN
Aircraft Certification Service
Washington, DC
U.S. Department of Transportation
Federal Aviation Administration
NM-09-18

March 11, 2009

This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) advises registered owners and operators of transport category airplanes equipped with carbon disc brakes of the possibility of moisture absorption and subsequent freezing during flight, resulting in tire failure and damage to the airplane on landing due to a locked wheel brake, and that corrective actions may impose additional cost.

Background

Following an extended period of heavy rain, a Bombardier Model BD-700 (Global Express) departed Van Nuys, California, from a dry runway for a long-range flight to London Luton Airport. During the subsequent landing roll, the left inboard main landing gear tire suffered a slide-through failure resulting from an initially locked wheel. This tire failure caused extensive damage to the flight control system. Although the aircraft landed safely, the investigation by the Air Accidents Investigation Branch (AAIB), United Kingdom, made the following safety recommendation:

AAIB Safety Recommendation 2008-073 recommends that the Federal Aviation Administration (FAA), the European Aviation Safety Agency (EASA), and Transport Canada Civil Aviation (TCCA) raise awareness of the vulnerability of carbon brakes to freezing in flight following exposure to moisture on the ground, emphasizing the significance of the slow drying rate of saturated brakes even in warm, low humidity conditions, Ref.1.

TCCA published Ref. 2. Service Difficulty Advisory AV-2008-08 to inform operators and flightcrew of airplanes equipped with carbon disc brakes of the possibility of moisture absorption and subsequent freezing during flight, resulting in tire failure and damage to the airplane on landing due to a locked wheel brake. After reviewing the available information, EASA concurred with the TCCA advisory and published Ref. 3 Service Information Bulletin SIB No. 2008-89.

The FAA has reviewed the information and concurs with the TCCA advisory and EASA SIB. We are issuing this SAIB to ensure that all owners, operators, and maintenance personnel of affected aircraft registered in the U.S. are aware of these recommendations.

Details of the BD700 Incident: TCCA was advised of an occurrence involving an airplane equipped with carbon disc brakes that landed with a locked wheel brake. During the landing rollout on a dry runway, the locked brake caused the associated tire to rupture. As the rollout continued, the wheel became free to rotate, causing the tire to shed and flail large portions which caused significant damage. The tire rupture resulted in the loss of two of three hydraulic systems, damage to the flap structure, and damage to electrical wiring, which controlled multi-function wing spoilers.

Prior to departure, the airplane was exposed to a significant amount of rainfall and the carbon disc brakes were soaked by water. The airplane taxied with minimal use of braking and took off under dry conditions about 12 hours after the rain had stopped. Automatic brake application occurred after landing gear retraction. Moisture on the contact faces of the brake froze as the airplane climbed to a high altitude in sub-freezing conditions.

The braking materials in the stators and rotors of carbon disc brakes are porous which allows them to absorb or retain moisture. After extensive water soaking, the brakes can be dried by a prolonged period of exposure to dry warm conditions or deliberate braking action during taxi to heat the brakes. If a wet brake is not heated sufficiently to evaporate moisture from the disc surfaces, there is a possibility that after in-flight cold soak or parking in freezing conditions, the brake surfaces may freeze together. In addition to exposure to environmental moisture, brakes may become soaked with water during washing if correct procedures to protect the brakes are not followed.

In this occurrence, the failed tire was of cross-ply construction. Tires of radial-ply construction do not possess the same failure mode, and detached debris is likely to be significantly smaller and lighter. However, it is still possible that debris from a radial-ply construction tire failure may damage the aircraft.

The FAA is evaluating the aforementioned information with regard to potential continued airworthiness concerns on U.S.-registered aircraft (e.g., the loss of braking during emergency situations). At this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.

Recommendations
  1. During taxi, use light brake applications to warm the brakes before takeoff.
  1. When landing, carry out a positive landing to ensure initial wheel spin-up and breakout of frozen brakes, if frozen brakes are suspected.
  1. Avoid touch-and-go landings, if frozen brakes are suspected.
  1. During the landing roll and subsequent taxi, use brakes to prevent progressive build-up of ice on the wheels and brakes. If equipped, monitor brake temperatures during taxi.
Following take-off or landing on wet, snow-covered, or slush-covered runways and taxiways, tires should be inspected for flat spots prior to the next flight.

Caution: Freezing of carbon disc brakes may occur prior to or following takeoff even though conditions prior to takeoff are not considered to be cold nor adverse weather operations (adverse weather conditions include rain, snow, or slush, or operations on taxiways and runways covered with these contaminants).

Reference Publications:
  1. Air Accidents Investigation Branch (AAIB), United Kingdom, Safety Recommendation 2008-073, dated December 4, 2008.
  1. Transport Canada Civil Aviation (TCCA) Service Difficulty Advisory AV-2008-08, dated December 2, 2008; http://www.tc.gc.ca/CivilAviation/certification/menu.htm.
  1. EASA Safety Information Bulletin SIB No. 2008-89, dated December 19, 2008; E-mail: ADs@easa.europa.eu.
For Further Information Contact

Mahinder Wahi, Aerospace Engineer, Transport Standards Staff, 1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone: 425-227-2142; fax: 425-227-1320; e-mail: mahinder.wahi@faa.gov.