[Federal Register Volume 59, Number 39 (Monday, February 28, 1994)] [Unknown Section] [Page ] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 94-4449] [Federal Register: February 28, 1994] ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION 14 CFR Part 39 [Docket No. 93-NM-126-AD] Airworthiness Directives; Boeing Model 747 Series Airplanes 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 certain Boeing Model 747 series airplanes. That action would have required modification of the automatic speed brake control circuit. Since the issuance of the NPRM, the Federal Aviation Administration (FAA) has reconsidered its position on this safety issue and has concluded that the proposed modification is unnecessary to provide an acceptable level of safety. Accordingly, the proposed rule is withdrawn. FOR FURTHER INFORMATION CONTACT: Kristin Larson, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-1760; fax (206) 227-1181. SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation Regulations to add a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, was published in the Federal Register on September 17, 1993 (58 FR 48616). The proposed rule would have required modification of the automatic speed brake control circuit. That action was prompted by a report of failure of a hydraulic pressure line to a landing gear truck tilt cylinder, which resulted in inadvertent deployment of the automatic speed brake. The proposed actions were intended to prevent inadvertent in-flight operation of the automatic speed brake system. Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. Boeing requests that the proposal be withdrawn. Boeing notes that an AD was not issued when the Boeing service bulletin (referenced in the notice) was released in 1971 because, at that time, neither Boeing nor the FAA considered that there was an unsafe condition addressed. Boeing has carefully examined the scenario of the incident of inadvertent deployment of the automatic speed brake that prompted issuance of the proposal, and finds that the incident did not occur during airline operations, but during a Boeing test flight. Specifically, the incident occurred while the airplane was conducting ``touch and go's'' (which are not allowed in airline operations), which allowed the landing gear trucks to move out of the fully tilted position and initiated extension of the automatic speed brake. The pilot immediately recognized this and retracted the spoilers manually. (On Boeing Model 747 series airplanes equipped with triple slotted flaps, once the spoilers are retracted, the hydraulic flow redirects to the flaps immediately, and the lift is regained with minimal altitude loss.) Boeing points out that, during this incident, the reported 6- foot loss in altitude occurred when the airplane was at around 100 feet. Finally, Boeing asserts that the reason for issuance of its service bulletin, containing procedures for installing the modification of the automatic speed brake control circuit, was not only to add better protection for the circuit, but to minimize the ``pitch up'' on the ground during landing. If the number four hydraulic system (which powers the inboard spoilers) is inoperative, a ``pitch up'' would occur with outboard spoilers only. Boeing asserts that the pilot can easily compensate for this condition by using his/her hand and the speed brake levers. Based upon the information discussed above, Boeing requests that the proposal be withdrawn. - In response to these comments, the FAA acknowledges that issuance of the notice was based on a recommendation of the Systems Review Task Force (SRTF). The SRTF has completed an extensive review process to ``* * * determine possible design concepts that will provide alternative means of control of flight critical functions in the event of total loss of all (normal) redundant systems which provide that control * * *'' The SRTF's charter was specifically oriented toward identifying alternative means to ensure controllability of airplanes that have lost all normal flight control functions, while maintaining basic airplane structural integrity. The SRTF recommended incorporation of the modification described in Boeing Service Bulletin 27-2066, Revision 1, dated August 20, 1971, which was referenced in the notice. However, after further study of the Boeing service bulletin and its intent, the FAA has determined that failure to incorporate the modification described in that service bulletin does not degrade the flight safety of the airplane. While the modification adds logic to prevent uncommanded deployment on touchdown for airplanes equipped with auto speed brakes, the effects of such deployment can be readily rectified by manually retracting the spoilers. Although the installation of the proposed modification would add additional protection against inadvertent deployment of the speed brakes and thereby minimize the pitch up on the ground as a result of such deployment, this condition does not cause loss of hydraulics, does not affect airplane symmetry, and does not significantly degrade airplane flight controllability. Upon further consideration, the FAA has determined that this condition does not present an unsafe condition that would warrant the proposed mandatory corrective action. Accordingly, the proposed rule is hereby withdrawn. Withdrawal of this notice of proposed rulemaking constitutes only such action, and does not preclude the agency from issuing another notice in the future, nor does it commit the agency to any course of action in the future. 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 93-NM-126- AD, published in the Federal Register on September 17, 1993 (58 FR 48616), is withdrawn. Issued in Renton, Washington, on February 22, 1994. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 94-4449 Filed 2-25-94; 8:45 am] BILLING CODE 4910-13-U
