[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 Accordingly, the proposed rule is withdrawn.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    Boeing requests that the proposal be withdrawn.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