02-18200. Airworthiness Directives; Boeing Model 777-200 Series Airplanes Equipped With General Electric Engines

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Proposed rule; withdrawal.

SUMMARY:

This action withdraws a notice of proposed rulemaking (NPRM) that proposed a new airworthiness directive (AD), applicable to all Boeing Model 777-200 series airplanes equipped with General Electric engines. That action would have required installation of a high-temperature silicone foam seal on the aft fairing of the strut. Since issuance of the NPRM, the Federal Aviation Administration (FAA) has received new information that indicates that the unsafe condition would not be prevented by the proposed action. Subsequently, the FAA has issued new rulemaking that positively addresses the unsafe condition identified in the NPRM and eliminates the need for the actions proposed by the NPRM. Accordingly, the proposed rule is withdrawn.

FOR FURTHER INFORMATION CONTACT:

Technical Information: John Vann, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone [phone]; fax [phone].

Other Information: Judy Golder, Airworthiness Directive Technical Editor/Writer; telephone [phone], fax [phone]. Questions or comments may also be sent via the Internet using the following address: [e-mail]. Questions or comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

SUPPLEMENTARY INFORMATION:

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to add a new airworthiness directive (AD), applicable to all Boeing Model 777-200 series airplanes equipped with General Electric engines, was published in the Federal Register as a Notice of Proposed Rulemaking (NPRM) on October 30, 2001 (66 FR 54727). The proposed rule would have required installation of a high-temperature silicone foam seal on the aft fairing of the strut. That action was prompted by reports indicating that, during routine inspections of the aft fairing of the strut, evidence of an elevated temperature in the interior cavity of the aft fairing was found on several Boeing Model 777-200 series airplanes equipped with General Electric engines. The proposed actions were intended to prevent primary engine exhaust from entering the aft fairing of the strut, elevating the temperature in the aft fairing of the strut, and creating a potential source of ignition, which could lead to an uncontrolled fire in the aft fairing of the strut. Such a fire would expose the wing fuel tank to high-temperature gasses and flames and result in a potential ignition source for the fuel tank, and reduced structural integrity of the wing.

Actions That Occurred Since the NPRM Was Issued

Since the issuance of that NPRM, one operator reported significant heat damage to the forward end of the diagonal brace on an airplane that had the high-temperature silicone foam seal installed. Investigation revealed that the foam seal was not a sufficient barrier to the heat of the primary engine exhaust. Thus the exhaust entered the aft fairing of the strut through a gap in the heat shield, elevating the temperature and resulting in heat damage to the primary fire seal, heat shield seal, and secondary fluid seal. The damaged seals allowed the exhaust to pass into the aft fairing cavity causing heat damage to the diagonal brace assembly.

As a result of this incident, the FAA has determined that the unsafe condition would not be prevented by the installation of the high temperature silicone foam seal alone, which the NPRM proposed to require.

Other Relevant Rulemaking

On March 29, 2002, the FAA issued AD 2002-07-07, amendment 39-12701 (67 FR 16991, April 9, 2002), applicable to certain Boeing Model 777-200 series airplanes equipped with General Electric GE90 series engines. That AD requires repetitive inspections of the diagonal brace and forward seals of the aft fairing of the strut to find discrepancies, and corrective actions, if necessary. The actions required by that AD are intended to prevent primary engine exhaust from entering the aft fairing of the strut and elevating the temperature, which could lead to heat damage of the seals and diagonal brace. Such damage could result in cracking and fracture of the forward attachment point of the diagonal brace, loss of the diagonal brace load path, and consequent separation of the strut and engine from the airplane.

FAA's Conclusions

In AD 2002-07-07, the FAA stated that it was considering withdrawing NPRM 2001-NM-93-AD. Upon further consideration, the FAA has determined that the unsafe condition addressed by that NPRM would NOT be prevented by the actions that would be required by that proposed AD, but WOULD be prevented by the actions required by AD 2002-07-07. Accordingly, the proposed rule is hereby withdrawn.

Withdrawal of this NPRM constitutes only such action, and does not preclude the agency from issuing another action in the future, nor does it commit the agency to any course of action in the future.

Regulatory Impact

Since this action only withdraws a notice of proposed rulemaking, it is neither a proposed nor a final rule and therefore is not covered under Executive Order 12866, the Regulatory Flexibility Act, or DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979).

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Withdrawal

Accordingly, the notice of proposed rulemaking, Docket 2001-NM-93-AD, published in the Federal Register on October 30, 2001 (66 FR 54727), is withdrawn.

Issued in Renton, Washington, on July 11, 2002.

Lirio Liu-Nelson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.