AD 96-04-11

Effective March 11, 1996.

Comments for inclusion in the Rules Docket must be received on or before April 23, 1996.

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.

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.

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 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.

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.

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.

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.

Air transportation, Aircraft, Aviation safety, Safety.

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:

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

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