[Federal Register Volume 61, Number 37 (Friday, February 23, 1996)]
[Rules and Regulations]
[Pages 6935-6937]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-3950]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-30-AD; Amendment 39-9523; AD 96-04-11]


Airworthiness Directives; Boeing Model 757-200 Series Airplanes 
Equipped With Rolls Royce Model RB211-535E4/E4B Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
is applicable to certain Boeing Model 757-200 series airplanes. This 
action requires a revision to the Airplane Flight Manual to ensure that 
the flightcrew activates the engine cowl thermal anti-ice (CTAI) system 
for both engines at the top of descent to avoid engine rundown (loss of 
engine power). This amendment is prompted by reports that, after the 
flightcrew activated the engine CTAI during descent, engine rundown 
occurred due to unknown reasons. The actions specified in this AD are 
intended to ensure that the flightcrew activates the engine cowl 
thermal anti-ice system for both engines prior to descent; activation 
of the engine CTAI system in the middle of descent could result in a 
compressor stall and subsequent engine rundown of multiple engines.

DATES: Effective March 11, 1996.
    Comments for inclusion in the Rules Docket must be received on or 
before April 23, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-30-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056.
    Information concerning this amendment may be obtained from or 
examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue 
SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT: Nancy Hanowski, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue SW., Renton, Washington; telephone (206) 227-
2684; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: The FAA has received at least seven reports 
of engine rundown (loss of engine power) on Boeing Model 757-200 series 
airplanes equipped with Rolls Royce Model RB211-535E4/E4B engines. 
These incidents occurred while the airplanes were in flight, at an 
altitude between 24,000 and 29,000 feet.
    In four of the seven incidents, dual engine events occurred in 
which one of the engines stalled and ``recovered'' to produce usable 
thrust; the other engine stalled, ran down to sub-idle power, and was 
subsequently shutdown.
    In six of the seven incidents, the flightcrew activated the engine 
cowl thermal anti-ice system (CTAI) for both engines during the middle 
of the descent, which resulted in either single or dual engine 
compressor stalls and subsequent engine rundowns.
    In the seventh incident, the flightcrew increased engine power from 
a minimum flight idle to a slightly higher power when both engines 
stalled; one of the engines returned to normal thrust level, and the 
other engine ran down to sub-idle power.
    The cause of these engine rundown incidents has not been 
conclusively proven. However, ice accumulation on the engine is one 
possible cause that is 

[[Page 6936]]
being investigated. Rolls Royce (the manufacturer of the subject 
engines) is continuing to conduct tests and evaluations to determine 
the exact cause of engine rundowns.

FAA's Considerations

    Data gathered from the reported incidents have led the FAA to 
consider that activation of the engine CTAI system for both engines 
during the middle of descent may result in a compressor stall and 
subsequent loss of multiple engine power. Operation of the engine at a 
higher idle thrust level, from the beginning of the descent, will 
increase the compressor stall margin and, thus, reduce the risk of 
compressor stall. A higher idle thrust level also will increase the 
airflow through the compressor and, thus, reduce the susceptibility of 
the compressor to rain and icing. Activation of the engine CTAI system 
at the beginning of descent has the effect of increasing the idle 
thrust level.
    Based on this, the FAA finds that, prior to idle descent above 
flight level (FL) 200 (20,000 feet), activation of the engine CTAI 
system for both engines is necessary in order to operate the engine at 
a higher idle thrust level. This action will reduce the risk of engine 
stall and rundown during idle descent.
    In addition, the FAA finds that, below FL 200, operation of the 
engine at low idle thrust level using normal engine CTAI system 
procedures will maintain the necessary icing protection for the engine 
and will provide adequate stall protection.

Explanation of the Requirements of the AD

    Since an unsafe condition has been identified that is likely to 
exist or develop on other Boeing Model 757-200 series airplanes, 
equipped with Rolls Royce Model RB211-535E4/E4B engines, of the same 
type design, this AD is being issued to ensure that the flightcrew 
activates the engine cowl thermal anti-ice system for both engines 
prior to descents above flight level (FL) 200. This AD requires 
revising the Limitations Section of the FAA-approved Airplane Flight 
Manual (AFM) to include information instructing the flightcrew to 
activate the engine cowl thermal anti-ice system for both engines prior 
to descent. The AFM limitation procedures will reduce the risk of a 
variety of suspected causes for engine rundown.
    This AD action is considered to be interim action. Rolls Royce has 
advised the FAA that it currently is developing a modification that 
will positively address the unsafe condition addressed by this AD for 
the various suspect causes. Once this modification is developed, 
approved, and available, the FAA may consider additional rulemaking.
    Since a situation exists that requires the immediate adoption of 
this regulation, it is found that notice and opportunity for prior 
public comment hereon are impracticable, and that good cause exists for 
making this amendment effective in less than 30 days.

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
this rule. Interested persons are invited to comment on this rule by 
submitting such written data, views, or arguments as they may desire. 
Communications shall identify the Rules Docket number and be submitted 
in triplicate to the address specified under the caption ADDRESSES. All 
communications received on or before the closing date for comments will 
be considered, and this rule may be amended in light of the comments 
received. Factual information that supports the commenter's ideas and 
suggestions is extremely helpful in evaluating the effectiveness of the 
AD action and determining whether additional rulemaking action would be 
needed.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the rule that might 
suggest a need to modify the rule. All comments submitted will be 
available, both before and after the closing date for comments, in the 
Rules Docket for examination by interested persons. A report that 
summarizes each FAA-public contact concerned with the substance of this 
AD will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this rule must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-30-AD.'' The postcard will be date stamped and 
returned to the commenter.
    The regulations adopted herein will not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    The FAA has determined that this regulation is an emergency 
regulation that must be issued immediately to correct an unsafe 
condition in aircraft, and that it is not a ``significant regulatory 
action'' under Executive Order 12866. It has been determined further 
that this action involves an emergency regulation under DOT Regulatory 
Policies and Procedures (44 FR 11034, February 26, 1979). If it is 
determined that this emergency regulation otherwise would be 
significant under DOT Regulatory Policies and Procedures, a final 
regulatory evaluation will be prepared and placed in the Rules Docket. 
A copy of it, if filed, may be obtained from the Rules Docket at the 
location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends part 39 of 
the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 USC 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

96-04-11  Boeing: Amendment 39-9523. Docket 96-NM-30-AD.

    Applicability: Model 757-200 series airplanes, equipped with 
Rolls Royce Model RB211-535E4/E4B engines; certificated in any 
category.
    Compliance: Required as indicated, unless accomplished 
previously. To reduce the risk of engine rundown during idle 
descents, accomplish the following:
    (a) Within 30 days after the effective date of this AD, revise 
the Limitations Section of the FAA-approved Airplane Flight Manual 
(AFM) to include the following statement. This may be accomplished 
by inserting a copy of this AD in the AFM.

``Limitations Section 1

    In order to reduce the risk of engine rundown during idle 
descents, activate the engine cowl thermal anti-ice system for both 
engines prior to idle descents above flight level (FL) 200. Below FL 
200, use normal engine cowl thermal anti-ice system procedures (as 
defined in the AFM).


[[Page 6937]]

    Note: The Master Minimum Equipment List (MMEL) for Model 757 
series airplanes currently specifies that an airplane may be 
dispatched with an engine anti-ice valve locked in the closed 
position. The requirement of this section to activate the engine 
cowl thermal anti-ice system prior to descent will prevent the 
dispatch of airplanes with an engine anti-ice valve locked in the 
closed or open position. Where differences exist between the current 
specification of the MMEL and the requirements of this AFM 
limitation, the AFM limitation prevails.''

    (b) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal 
Operations Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 1: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (c) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.
    (d) This amendment becomes effective on March 11, 1996.

    Issued in Renton, Washington, on February 15, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-3950 Filed 2-22-96; 8:45 am]
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