SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites interested people to take part in this rulemaking by sending written comments, data, or views. The most helpful comments reference a specific portion of the proposed special conditions, explain the reason for any recommended change, and include supporting data.

The FAA will consider all comments received by the closing date for comments, and will consider comments filed late if it is possible to do so without incurring delay. The FAA may change these special conditions based on the comments received.

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Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in title 14, Code of Federal Regulations (14 CFR) 11.35, the FAA will post all comments received without change to www.regulations.gov, including any personal information you provide. The FAA will also post a report summarizing each substantive verbal contact received about these special conditions.

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Confidential Business Information (CBI) is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to these special conditions contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to these special conditions, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and the indicated comments will not be placed in the public docket of these proposed special conditions. Send submissions containing CBI to the individual listed in the For Further Information Contact section above. Comments the FAA receives, which are not specifically designated as CBI, will be placed in the public docket for these proposed special conditions.

Background

On November 16, 2021, P&WC applied for a type certificate for its new Model aircraft engine model PW220A. The PW220A is a turboshaft engine designed for transport category twin-engine helicopters.

Under 14 CFR 21.17(c), an application for type certification is effective for three years, unless the FAA approves a longer period. Section 21.17(d) provides that, where a type certificate has not been issued within the time limit established under §  21.17(c), the applicant may file for an extension and update the designated applicable regulations in the type certification ( printed page 54840) basis. Since the project was not certificated within the established time limit, the FAA approved a request for extension by P&WC, which reapplied on May 7, 2025. Their request was approved and the FAA determined the type certification basis established on November 19, 2021 is unaffected.

Type Certification Basis

Under the provisions of 14 CFR 21.17, P&WC must show that the Model PW220A aircraft engine meets the applicable provisions of part 33, as amended by amendments 33-1 through 33-34.

If the Administrator finds that the applicable airworthiness regulations ( e.g.,14 CFR part 33) do not contain adequate or appropriate safety standards for the Model PW220A because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, these special conditions would also apply to the other model under § 21.101.

The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with 14 CFR 11.38, and they become part of the type certification basis under § 21.17(a)(2).

Novel or Unusual Design Features

The P&WC Model aircraft engine model PW220A will incorporate the following novel or unusual design feature:

An unusual power rating structure that includes an ICR.

Discussion

The PW220A engine is a new centerline turboshaft engine designed for a transport category, twin-engine helicopter. The applicant has requested that operation will include an ICR where the power from one engine will be reduced to a low idle condition while the other engine will provide 100% of the required power to the aircraft during cruise flight. The applicant is requesting a rating structure such that the PW220A engine in ICR will have different limits from the all-engines-operating (AEO) or one-engine-inoperative (OEI) conditions.

The applicable airworthiness requirements do not contain the ICR definition and do not contain adequate or appropriate safety standards for the type certification of these new and unusual engine ratings.

The inclusion of the ICR will have implications on multiple regulatory sections affecting both engine operation and continued airworthiness which must be assessed by the FAA.

The prime objective of ICR is to reduce total fuel consumption and increase the operating range of the helicopter. The fundamental concept of ICR stems from the fact that one engine is thermodynamically more efficient at providing a given total power than two engines sharing the load equally. As such, it is beneficial from a fuel savings point of view to bring one engine to minimum fuel flow (the stand-by engine) and use the other engine to provide 100% of the required power to the aircraft during the cruise phase of the flight (the active engine). The lower the stand-by condition, the higher the benefit in fuel consumption.

The proposed special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

Applicability

As discussed above, these proposed special conditions are applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, these special conditions would apply to the other model as well.

Conclusion

This action affects only a certain novel or unusual design feature on the PWC aircraft engine model PW220A. It is not a rule of general applicability.

Authority Citation

The authority citation for these special conditions is as follows:

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

The Proposed Special Conditions

Accordingly, the Federal Aviation Administration (FAA) proposes the following special conditions as part of the type certification basis for Pratt and Whitney Canada Model PW220A engine.

Section 1.1 General Definitions

The following definitions are added to § 1.1:

ICR mode of operation means one engine is providing 100% of the required power to the rotorcraft for cruise flight, and the other engine is in Rated ICR stand-by power for a two-engine rotorcraft.

Rated ICR stand-by power means, with respect to rotorcraft turbine engines, the approved lowest engine rpm at which the engine can safely operate while in the ICR mode of operation.

Rated ICR active maximum continuous power means, with respect to rotorcraft turbine engines, the approved brake horsepower developed statically or in flight in standard atmosphere at a specified altitude within the engine operating limitations established under 14 CFR, part 33 and approved for unrestricted periods of use while in the ICR mode of operation.

Rated ICR 2 minute power means, with respect to rotorcraft turbine engines, the approved brake horsepower developed under static conditions at specified altitudes and temperatures within the engine operating limitations established under 14 CFR, part 33 for periods not longer than 2 minutes while in the ICR mode of operation. There is no mandatory inspection or prescribed maintenance action required after reaching this power level.

Section 33.7 Engine Ratings and Operating Limitations

In addition to the requirements of section 33.7(c), ratings and limitations are established for horsepower, torque, r.p.m., gas temperature, time duration, and number of occurrences for rated ICR active maximum continuous power and rated ICR 2 minute power.

Section 33.28 Engine Control Systems

The requirements of § 33.28 except that § 33.28(i)(2) should read as follows:

When an engine dedicated electrical power source is required for compliance with paragraph (i)(1) of this section, its capacity should provide sufficient margin to account for engine operation below the rated ICR stand-by power, where the engine control system is designed and expected to recover engine operation automatically.

Section 33.68 Induction System Icing

The requirements of § 33.68, except that “minimum descent idle rotor speeds” is replaced with the “rated ICR stand-by power rotor speeds” in § 33.68(a) and § 33.68(b).

Section 33.73 Power or Thrust Response

The requirements of § 33.73, except § 33.73(b) should read as follows:

The design and construction of the engine must enable an increase from the ( printed page 54841) rated ICR stand-by power lever position to 95 percent rated takeoff power in not over 5 seconds. The 5-second power response must occur from a stabilized static condition using only the bleed air and accessories loads necessary to run the engine.

Section 33.78 Rain and Hail Ingestion

The requirements of § 33.78, except §§ 33.78(b)(1) through 33.78(b)(4) should read as follows:

(1) A normal stabilization period of three minutes at rated maximum continuous power without rain ingestion, followed immediately by the suddenly commencing ingestion of rain for three minutes at rated maximum continuous power, then

(2) Continuation of the rain ingestion during subsequent rapid deceleration to the rated ICR stand-by power, then

(3) Continuation of the rain ingestion during three minutes at the rated ICR stand-by power, then

(4) Continuation of the rain ingestion during subsequent rapid acceleration to rated ICR 2 minute power.

Section 33.87 Endurance Test

The requirements of § 33.87, except as follows:

(1) The requirements of § 33.87(d)(1) except that instead of alternating between rated takeoff power and idling power:

(i) The higher condition must be rated takeoff power during the first, second and fourth periods and rated ICR 2 minute power during the third, fifth and sixth periods.

(ii) The lower condition must be the rated ICR stand-by power condition or lower.

(iii) During the sixth period, lower condition must be kept for 10 minutes instead of 5 minutes.

(2) The requirements of § 33.87(d)(2) through § 33.87(d)(7), except as follows:

(i) The first 15 of the twenty-five 6-hour test cycles required by § 33.87(d)(2) must be conducted at the rated ICR active maximum continuous power instead of the rated maximum continuous power.

(ii) In the last 10 of the twenty-five 6-hour test cycles, the last 5 minutes of the 1 hour at the rated continuous OEI power required by § 33.87(d)(3), must be run at the rated ICR 2 minute power instead of the rated continuous OEI power.

(iii) The test required by § 33.87(d)(4) must be performed for 55 minutes instead of 60 minutes and must be performed as follows: rated maximum continuous power for 30 minutes, followed by the rated ICR active maximum continuous power for 25 minutes.

(iv) The two hours of incremental cruise power required by § 33.87(d)(5) must be conducted between the rated ICR active maximum continuous power and the ground or minimum idle rotational speed.

(v) The thirty minutes of accelerations and decelerations required by § 33.87(d)(6) must be conducted as follows:

a. The higher condition must be the rated takeoff power during the first and fourth period and the rated ICR 2 minute power during the second, third, fifth and sixth periods.

b. The lower condition must be the rated ICR stand-by power condition or lower.

Section 33.89 Operation Test

The requirements of § 33.89, except § 33.89(a)(3) should be as follows:

The minimum power response time to 95% rated takeoff power, from power lever positions representative of rated ICR stand-by power condition and of minimum flight idle, starting from stabilized idle operation, under the following engine load conditions:

i. No bleed air and power extraction for aircraft use.

ii. Maximum allowable bleed air and power extraction for aircraft use.

iii. An intermediate value for bleed air and power extraction representative of that which might be used as a maximum for aircraft during approach to a landing.

91 FR 54839