Airworthiness Standards: Rotorcraft Engine Rotor Burst Protection

SUMMARY: This final rule amends the airworthiness regulations to

require that manufacturers of new design transport category rotorcraft

minimize the adverse effects of a turbine engine rotor failure. Turbine

engine rotor failures have occurred resulting in the release of high

energy engine rotor fragments or other engine component fragments.

These fragments have damaged critical rotorcraft structures, systems,

controls, and adjacent engines, as well as caused serious or fatal

injuries to passengers and crewmembers. This action is intended to

minimize these hazards.

EFFECTIVE DATE: January 31, 1996.

FOR FURTHER INFORMATION CONTACT:

Mr. Ron Dalton, Federal Aviation Administration (FAA), Rotorcraft

Directorate, Rotorcraft Standards Staff, Fort Worth, TX 76193-0110,

telephone (817) 222-5127.

SUPPLEMENTARY INFORMATION:

Background

A Notice of Proposed Rulemaking (NPRM) No. 89-29 was published in

the Federal Register on October 17, 1989 (54 FR 42716), and the comment

period was reopened by NPRM No. 89-29A, published in the Federal

Register on January 14, 1993 (58 FR 4566). These NPRMs proposed to

amend 14 CFR part 29 (part 29) to require designs that would minimize

the hazards associated with the failures of turbine engine (engine)

rotors in newly designed transport category rotorcraft. Since there has

not been an adverse service history for normal category rotorcraft,

similar changes to 14 CFR part 27 were not proposed. If an adverse

service history for normal category rotorcraft should develop, similar

changes to 14 CFR part 27 would be considered.

National Transportation Safety Board (NTSB) Recommendation

This amendment responds to NTSB Safety Recommendation A-84-60 dated

June 14, 1984. The NTSB recommends that the FAA review engine

compartment design of all U.S. type certificated ``multiengined

helicopters with regard to the probability that an uncontained engine

failure will result in catastrophic damage to the drive train,

electrical, and/or fuel and hydraulic system components.'' This rule

responds directly to the recommendation.

Provisions of NPRM Nos. 89-29 and 89-29A

NPRM No. 89-29 proposed changes to 14 CFR 29.901 and 29.903

(Secs. 29.901 and 29.903) to increase the safety margin by requiring

designs that minimize the hazards to transport category rotorcraft in

the event of an engine rotor failure. The required designs may include

items such as separation or duplication of critical components, engine

location to reduce risk, or placement of critical components in benign

locations. Containment provisions for one or more stages of the engine

were not specifically proposed by that proposal; however, as stated in

Notice No. 89-29A, containment provisions could be one of several

effective means of compliance.

NPRM No. 89-29A reopened the comment period and invited comments

only on the issues of engine rotor containment and the use of advanced

composite material. NPRM No. 89-29A also provided further clarification

of the intent of the NPRM. Specifically, the FAA clarified that when

evaluating an applicant's proposed method of compliance, the FAA would

consider the available technology and the costs required to minimize

the hazards from an engine rotor failure. The FAA also noted that

engine rotor containment features have not been specifically required

in airplane designs that comply with 14 CFR 23.903 and 25.903

(Secs. 23.903 and 25.903). Likewise, containment features would not be

specifically required in rotorcraft to minimize the hazards of an

engine rotor failure. The guidance contained in Advisory Circular (AC)

20-128, ``Design Considerations for Minimizing Hazards Caused by

Uncontained Turbine Engine and Auxiliary Power Unit Rotor and Fan Blade

Failures,'' is applicable to the requirements of Sec. 29.903 in the

same way it now applies to Secs. 23.903 and 25.903 for airplanes.

Furthermore, the guidance in AC-29-2A, ``Certification of Transport

Category Rotorcraft,'' supplements that in AC 20-128.

Comments to NPRM Nos. 89-29 and 89-29A

Three commenters fully supported the proposals of NPRM No. 89-29.

Three other commenters, including the Aerospace Industries Association

(AIA), requested that the NPRM be withdrawn because they believed it

strongly implied that the intent of the proposed rule was to require

the designer to eliminate the hazards associated with the failure of an

engine rotor through the use of containment devices made of advanced

composite material. As discussed above, it was not the intent of NPRM

No. 89-29 to require containment or the use of advanced composite

materials; containment devices made of composite materials could be one

means of compliance. Since this was unclear to the three commenters,

several meetings with representatives of AIA were held. Subsequently,

the FAA issued NPRM No. 89-29A, which reopened the comment period with

a further explanation of the proposed amendments.

Two comments were received in response to NPRM No. 89-29A. Neither

commenter addressed the issues of engine rotor containment or the use

of advanced composite material. As stated earlier in this document,

request for comments on these issues was the reason for reopening the

comment period for NPRM No. 89-29A.

One commenter simply restated an opinion submitted in response to

NPRM No. 89-29 that minimizing hazards resulting from engine rotor

failures in helicopters is impractical. The other commenter disagreed

with the proposed wording of Sec. 29.903. The commenter observed that

the wording, ``Design procedures must be taken to minimize the hazards

to the rotorcraft in the event of an engine rotor failure * * *,'' has

been applied to fixed wing aircraft for some time with little or no

success. The FAA disagrees that minimizing the hazards of engine rotor

failure is impractical or that compliance with similar requirements for

airplanes has not been successful. Based on a review of rotorcraft

service history and engineering studies, the FAA concludes that the

need for this amendment has been adequately demonstrated and shown to

be practical for rotorcraft.

The proposed change to Sec. 29.903 was inadvertently stated as

revising paragraph (f). The correct cite should have been to paragraph

Sec. 29.903(d). This error is corrected in this final rule. The FAA

adopts the changes to Secs. 29.901 and 29.903 as proposed, except for

the noted paragraph correction.

Regulatory Evaluation Summary

Proposed changes to Federal regulations must undergo several

economic analyses. First, Executive Order 12866 directs that each

Federal

[[Page 55775]]

agency shall propose or adopt a regulation only upon a reasoned

determination that the benefit of the intended regulation justify its

costs. Second, the Regulatory Flexibility Act of 1980 requires agencies

to analyze the economic effect of regulatory changes on small entities.

Third, the Office of Management and Budget directs agencies to assess

the effects of regulatory changes on international trade. In conducting

these analyses, the FAA has determined that this rule: (1) Will

generate benefits that justify its costs and is not a ``significant

regulatory action'' as defined in the Executive Order; (2) is not

significant as defined in DOT's Regulatory Policies and Procedures; (3)

will not have a significant impact on a substantial number of small

entities; and (4) will not constitute a barrier to international trade.

These analyses, available in the docket, are summarized below.

Costs

On the basis of estimates from FAA and industry, incremental

development and certification costs are estimated to be $33,600 per

type certification project. Incremental manufacturing costs are

estimated to be $560 for each single-engine rotorcraft and $1,120 for

each twin-engine rotorcraft.

In addition to increasing the acquisition costs of newly

certificated rotorcraft, the rule could result in weight penalties. FAA

and industry analyses suggest that this weight penalty could be as much

as 6 pounds per engine. Each additional pound of weight increases fuel

consumption for an average part 29 rotorcraft by approximately 0.0597

gallons per flight hour. Assuming 527 flight hours per year for an

average part 29 rotocraft, compliance with the rule will increase

annual fuel consumption by about 31.46 gallons per pound of additional

weight. Using a forecast jet fuel price of $1.78 per gallon, annual

fuel costs could rise by about $56 per additional pound, or about $366

per single engine transport rotorcraft, or $672 per twin-engine

transport rotorcraft, respectively, per year.

Assuming a production run of 15 years during which 10 aircraft are

produced per year and assuming that each rotorcraft has an operating

life of 15 years, the average costs of compliance are $5,824 for a

single-engine rotorcraft and $11,425 for a twin-engine rotorcraft.

Applying a discount rate of 7 percent, the average costs of compliance

for single-engine and twin-engine rotorcraft are $2,271 and $4,326,

respectively, at present value.

Benefits of Prevented Rotorcraft Damage and Loss

The assessment of the hazards of uncontained turboshaft engine

rotor bursts is based on data from the FAA, the Society of Automotive

Engineers (SAE), and the National Transportation Safety Board (NTSB).

For the period 1984 through 1989, in a sample representing 35.4 million

flight hours and 44.3 million hours of engine operation, the FAA/SAE

Committee on Uncontained Turbine Engine Rotor Events identified 68

engine rotor separation events, which resulted in the escape of rotor

fragments through the engine casing or the inlet structure. Thirty-

eight of those 68 events culminated in damage to rotorcraft structure

or systems (other than the engine itself) or injuries to occupants. Of

these, 17 events involved the release of turbine disk or spacer

fragments which directly resulted in substantial damage to or loss of

the aircraft. In the remaining 21 cases, damage and/or injuries were

not directly attributed to the uncontained failure, but were ascribed

to other causes. These 21 cases are excluded from the benefit

calculations.

Assuming 527 annual airborne hours for an average part 29

rotorcraft, FAA estimates the annual average probabilities that a

transport rotorcraft will be substantially damaged or destroyed as a

direct result of an uncontained turbine rotor burst are 0.00012 and

0.00066 for single- and twin-engine rotorcraft respectively.

The benefits of prevented rotorcraft damage and loss are the

avoided replacement and repair costs that would otherwise be incurred

in the absence of compliance with this rule. In this analysis, average

new unit costs of single- and twin-engine part 29 rotorcraft are

estimated to be $3.200 million and $4.275 million respectively.

Replacement cost is assumed to equal one-half the original new list

price, and restoration cost is estimated to be 13 percent of

replacement cost. The expected annual per-aircraft benefit of prevented

rotorcraft damage and loss is the weighted sum of replacement and

restoration costs where the weights are determined by the respective

probabilities of aircraft damage or loss. The FAA/SAE data included 2

single-engine rotorcraft destroyed, and 4 single-engine rotorcraft

damaged, in 26.6 million flight hours; it also included 4 twin-engine

rotorcraft destroyed, and 7 twin-engine rotorcraft damaged, in 8.8

million flight hours. The FAA concludes that the annual average

benefits of prevented rotorcraft damage are about $80 for single-engine

rotorcraft and $628 for twin-engine rotorcraft.

Under the same production run, operating life, and discount rate

assumptions used to derive average costs, the FAA estimates the

expected benefits of prevented aircraft damage/loss are $1,197 per

single-engine rotorcraft and $9,413 per twin-engine rotorcraft, or $412

and $3,243 at present value, respectively.

Benefits of Prevented Injuries and Fatalities

Using data from the FAA and the NTSB, the FAA identified five

fatalities and eight injuries resulting from the uncontained events

documented by the FAA/SAE Committee. Two of the fatalities occurred as

the result of a failed autorotation landing involving a single-engine

category B rotorcraft. In this case, the rotor burst did not directly

cause the failed landing and, therefore, the fatalities were excluded

from this analysis. The remaining three fatalities and three of the

injuries occurred in twin-engine rotorcraft. Five of the injuries

occurred in single-engine rotorcraft. Based on the available casualty

history, the FAA concludes that in 8.8 million twin-engine part 29

rotorcraft flight hours, the rule could prevent 3 fatalities, 1 serious

injury, and 2 minor injuries. The FAA also concludes that in 26.6

million single-engine part 29 rotorcraft flight hours, the rule could

prevent 2 serious injuries and 3 minor injuries.

Assuming 527 annual flight hours for a typical part 29 rotorcraft,

and based on costs of $2.5 million, $640,000 and $5,000 per each

fatality, serious injury, and minor injury, respectively, the average

annual benefits derived from avoiding fatalities and injuries are about

$488 per twin-engine transport rotorcraft and $26 per single-engine

rotorcraft.

Using the production run, operating life, discount rate, and other

assumptions listed above, the FAA estimates that the benefits of

avoided injuries and fatalities are $385 per single-engine rotorcraft,

and $7,321 per twin-engine rotorcraft, or $133 and $2,523 at present

value, respectively.

Cost-Benefit Summary

With respect to twin-engine rotorcraft, the benefits of avoided

aircraft damage and avoided fatalities and injuries are expected to

exceed the estimated development, certification, manufacturing and

operating costs of the rule by a margin of roughly 1.3 to 1 ($5,766 to

$4,326 in present value terms).

[[Page 55776]]

The benefits for single-engine rotorcraft, however, are less clear.

Because part 29 rotorcraft type-certificate applications for single

engine rotorcraft are unlikely, FAA's economic analysis of single-

engine types concludes that the rule will be cost-beneficial only if

design and manufacturing costs are modest. It should be noted that the

analysis of the benefits of prevented injuries and fatalities,

summarized above, does not assume that a fatality from operation of a

single-engine part 29 rotorcraft would be prevented; therefore, the

prevention of one fatality that would have occurred but for compliance

with this rule, would make benefits clearly exceed costs.

International Trade Impact Statement

The rule will have little or no effect on trade for either U.S.

firms marketing rotorcraft in foreign markets or foreign firms

marketing rotorcraft in the U.S. Each applicant for a new type

certificate for a transport category rotorcraft, whether the applicant

be U.S. or foreign, will be required to show compliance with this rule.

The rule harmonizes with proposed European Joint Aviation Requirements.

Regulatory Flexibility Determination

The Regulatory Flexibility Act (RFA) of 1980 was enacted by

Congress to ensure that small entities are not unnecessarily or

disproportionately burdened by Government regulations. The RFA requires

a Regulatory Flexibility Analysis if a rule is expected to have a

``significant economic impact on a substantial number of small

entities.''

Based on the standards and thresholds specified in implementing FAA

Order 2100.14A, Regulatory Flexibility Criteria and Guidance, the FAA

has determined that the rule will not have a significant impact on a

substantial number of small entities, because there are no ``small

entity'' rotorcraft manufacturers, as defined in the order.

Federalism Implications

The regulations 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 regulation will not have

sufficient federalism implications to warrant the preparation of a

Federalism Assessment.

Conclusion

For the reasons discussed above, and based on the findings in the

Regulatory Flexibility Determination and the International Trade Impact

Analysis, the FAA has determined that this regulation is not a

significant regulatory action under Executive Order 12866. In addition,

the FAA certifies that this regulation will not have a significant

economic impact, positive or negative, on a substantial number of small

entities under the criteria of the RFA. This regulation is not

considered to be significant under DOT Order Regulatory Policies and

Procedures (44 FR 11034; February 26, 1979). A final regulatory

evaluation of the regulation, including a final Regulatory Flexibility

Determination and International Trade Impact Analysis, has been placed

in the docket. A copy may be obtained by contacting the person

identified under FOR FURTHER INFORMATION CONTACT.

List of Subjects in 14 CFR Part 29

Air transportation, Aircraft, Aviation safety, Rotorcraft, Safety.

The Amendment

Accordingly, the FAA amends part 29 of the Federal Aviation

Regulations (14 CFR part 29) as follows:

PART 29--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT

1. The authority citation for part 29 is revised to read as

follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

2. Section 29.901 is amended by revising paragraph (c) to read as

follows:

Sec. 29.901 Installation.

* * * * *

(c) For each powerplant and auxiliary power unit installation, it

must be established that no single failure or malfunction or probable

combination of failures will jeopardize the safe operation of the

rotorcraft except that the failure of structural elements need not be

considered if the probability of any such failure is extremely remote.

* * * * *

3. Section 29.903 is amended by revising paragraph (d) to read as

follows:

Sec. 29.903 Engines.

* * * * *

(d) Turbine engine installation. For turbine engine installations--

(1) Design precautions must be taken to minimize the hazards to the

rotorcraft in the event of an engine rotor failure; and

(2) The powerplant systems associated with engine control devices,

systems, and instrumentation must be designed to give reasonable

assurance that those engine operating limitations that adversely affect

engine rotor structural integrity will not be exceeded in service.

* * * * *

Issued in Washington, DC, on October 6, 1995.

David R. Hinson,

Administrator.

[FR Doc. 95-27225 Filed 11-1-95; 8:45 am]

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