FAA Publishes Two ADs on Q400
After it received reports of cracking in the barrel nuts at the four primary front spar wing-to-fuselage attachment joints of the Bombardier Q400, the Federal Aviation Administration issued an AD to detect and correct cracking of the barrel nuts, which could result in reduced structural integrity of the wing-to-fuselage attachments and consequent detachment of the wing. This AD became effective February 13, 2008.
In addition, the agency received a reported case of failure of a bracket (P/N 85217732-108) of the over-centering spring assembly inside the translating door of the forward baggage compartment, prompting an additional Q-400 AD. This condition can exist on other translating doors on the aircraft. Investigation concluded that an insufficient gap between the bottom eyebolt and the barrel of the spring assembly caused an increase of tension load on the bracket and resulted in subsequent failure of the bracket. Failure of the bracket caused the eyebolt at the bottom of the spring assembly to become loose, resulted in damage of the support beam during normal door handle movement. Damage of the support beam, which is dormant, in combination with failure of a doorstop attached to any remaining undamaged support beam will degrade the structural integrity of the door, resulting in possible depressurization or loss of the door. This AD becomes effective March 20, 2008.
The bolt AD requires the inspection of all barrel nuts to determine if they have a certain markings, inspection of affected bolts to determine if the bolts are pre-loaded correctly, and replacement of all hardware if the pre-load is incorrect. For airplanes on which the pre-load is correct, the AD requires doing repetitive visual inspections for cracking of the barrel nuts and cradles and replacing all hardware for all cracked barrel nuts. It also requires replacement of all hardware for certain affected barrel nuts that do not have cracking, which would end the repetitive inspections for those airplanes and provides an optional replacement for all affected barrel nuts.
The AD was prompted by notification from Transport Canada Civil Aviation (TCCA) that an unsafe condition may exist on certain Q400s. During scheduled maintenance, an operator found cracks in the barrel nut at one of the four primary front spar wing-to-fuselage attachment joints. Investigation determined that the cracks were owing to hydrogen embrittlement and that the problem is likely restricted to a batch of 166 barrel nuts from one supplier. In addition, another operator has reported finding cracked barrel nuts at three of the four wing front spar wing-to-fuselage joints on one aircraft. All three barrel nuts were from the suspect batch. Cracking of the barrel nuts, if not detected and corrected, could result in reduced structural integrity of the wing-to-fuselage attachments and consequent detachment of the wing.
The Canadian emergency airworthiness directive recommends accomplishing the inspection of the barrel nuts within 100 flight hours. FAA, however, wants the inspection done within 50 flight hours, citing the degree of urgency associated with addressing the unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the required inspections. The FAA considers the AD interim action and is considering requiring the replacement of all hardware for all barrel nuts identified with a marking of LH7940T SPS 01, as required by the Canadian emergency airworthiness directive. However, the planned compliance time for the replacement would allow enough time to provide notice and opportunity for prior public comment on the merits of the modification. In order to ensure continued operational safety in the interim, this AD requires repetitive inspections for cracking of the suspect barrel nuts every 100 flight hours until the replacement is done.
On the door problem, the agency issued a notice of proposed rulemaking (NPRM) published on November 13, 2007. Corrective actions include a one-time inspection for damage of the spring support bracket and support beam of the forward baggage door, aft service door, and aft passenger door; repetitive inspections for integrity (corrosion, damage, cracking, and looseness or misalignment) of the doorstops of support beams found to be within damage limits; repair of support beams, or replacement of damaged brackets, support beams, or doorstops, as applicable; and removal of certain washers and nuts.
FAA estimates about 29 products of U.S. registry and each would take about five work-hours to comply with the basic requirements of this AD. Based on these figures, the cost estimate to U.S. operators to be $11,600, or $400 per product.

ATR 42-500 AD on Insulation Blankets
Despite having no aircraft affected by its AD are under U.S. register, the FAA is adopting a new airworthiness directive (AD) for certain ATR Model ATR42-500 series airplanes requiring the removal of metallized polyethylene terephtalate (MPET) insulation blankets installed on the left and the right sides of the airplane over frame 24 between stringers five and 14. This AD results from notification from European Aviation Safety Agency (EASA). There have been reports of two in-service aircraft where burnt spots were found on the insulation blankets installed over frame 24. Investigations concluded that owing to the presence of the bleed air duct, installation of the thermal-acoustical insulation blankets having an MPET, made the covering at this location unsafe. Such MPET insulation blankets, if not removed, could propagate a small fire that is the result of an electrical arc and could lead to a much larger fire, as happened in the SAS crash in the late 1990s. This AD becomes effective February 20, 2008.
ATR issued Service Bulletin ATR42-25-0155, dated April 10, 2007, describing procedures for removing the insulation blankets. The EASA mandated the service information and issued emergency airworthiness directive 2007-0106-E, dated April 18, 2007, to ensure the continued airworthiness of these airplanes in the European Union.
If an affected airplane is imported and placed on the U.S. Register in the future, the required action would take about six work hours per airplane and cost $480 per aircraft.