[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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