Skip to Content


Proposed Issuance of Policy Memorandum, Notice of Compliance With the Engine Ingestion Requirements Applicable to Turbine Powered, Part 23, Normal, Utility, Acrobatic, and Commuter Category Airplanes

Document Details

Information about this document as published in the Federal Register.

Published Document

This document has been published in the Federal Register. Use the PDF linked in the document sidebar for the official electronic format.

Start Preamble


Federal Aviation Administration, DOT.


Notice of policy statement; request for comments.


This document proposes to adopt new policy for compliance with the engine ingestion requirements applicable to turbine powered, normal, utility, acrobatic, and commuter category airplanes.


Comments submitted must be received no later than October 2, 2000.


Send all comments on this proposed policy statement to the individual identified under FOR FURTHER INFORMATION CONTACT.

Start Further Info


Randy Griffith, Federal Aviation Administration, Small Airplane Directorate, Regulations and Policy Branch, ACE-111, 901 Locust, Room 301, Kansas City, Missouri 64106; Start Printed Page 53339telephone (816) 329-4126; fax (816) 329-4090; email: <>.

End Further Info End Preamble Start Supplemental Information


Comments Invited

We invite your comments on this proposed policy statement, ACE-00-23.901(d)(2). You may submit whatever written data, views, or arguments you choose. You should mark your comments, “Comments to policy statement ACE-00-23.901(d)(2),” and submit in duplicate to the above address. We will consider all comments received on or before the closing date. We may change the proposals contained in this notice in light of the comments received.

You may also send comments via the Internet using the following address: Comments sent via fax or the Internet must contain “Comments to policy statement ACE-00-23.901(d)(2)” in the subject line. You do not need to submit in duplicate. Writers should format in Microsoft Word 97 or ASCII any file attachments that are sent via the Internet.

Submit comments using the following format:

  • Organize comments issue-by-issue. For example, discuss a comment concerning design evaluation and a comment about maintenance as two separate issues.
  • For each issue, state what specific change you are requesting to the proposed policy memorandum.
  • Include justification (for example, reasons or data) for each request.

The Proposed Policy


The current § 23.901(d)(2) requirement was incorporated by Amendment 23-53. However, the basic requirement, which has evolved into the current § 23.901(d)(2), was incorporated by Amendment 23-18.

Amendment 23-18 required that the engine installation provide continued engine operation without a sustained loss of power when operated at flight idle in rain for at least three minutes. The rate of rain ingestion was to be not less than 4 percent, by weight, of the engine induction airflow rate. The rule was incorporated due to reports of turbine engine power loss while operating in heavy rain. The intent of the rule was twofold: (1) To ensure that installation effects do not result in deterioration of the engine's rain ingestion tolerance determined by engine certification, and (2) to evaluate the engine's capability for rain ingestion for engines that were certificated before Amendment 33-6 since rain ingestion requirements were not added to 14 CFR part 33 until Amendment 33-6. Therefore, the rate of rain ingestion to be considered was based upon the part 33 engine certification requirement at the time.

Revisions of Standards

Amendment 23-29 revised the requirement to consider rated takeoff power/thrust. Also, the preamble to Amendment 23-29 further defined the intent of § 23.901(d)(2) by specifically stating that the rule is to ensure that installation effects do not result in any deterioration of the powerplant rain ingestion tolerance. Therefore, compliance with § 23.901(d)(2) required a separate determination for engine installation other than the requirements addressed by part 33 (for example, engine certification without further installation certification is inadequate to demonstrate compliance with the part 23 requirement).

Amendment 23-43 added a requirement that the installation be evaluated at the maximum installed power/thrust for takeoff. This new requirement was due to engine installations where rated takeoff power could be less than installed takeoff power; for example, de-rate thrust. The amendment also added a requirement that the engine be accelerated and decelerated safely under the rain conditions; however, Amendment 23-51 removed this consideration.

Amendment 23-53 added the current rule. The current amendment requires the installed engine to withstand ingestion of rain, hail, ice, and birds at a level not less than that established under engine certification. The significant changes with the new rule include operating concerns other than loss of power (for example, engine surges), the addition of hail, ice, and bird ingestion requirements, and replacement of specific rain quantification with the conditions used during engine certification. Under Amendment 23-53, the airplane applicant needs to evaluate the conditions used to address rain, hail, ice, and bird ingestion during engine certification and how the installation relates to these conditions.

Means of Compliance

When showing compliance with the rain ingestion requirements for all amendment levels of § 23.901(d)(2), compliance is typically accomplished with design analysis that identifies areas of concern and test. Items that you should consider when evaluating the installation include: Areas where water pooling (for example, inlet system channels, indentations, and so forth, typical of turbopropeller type inlets) or water shed (for example, wings directing water into the inlet system typical of engines mounted behind the wings) may occur. Areas such as these could cause localized “slugs” of water ingestion that would not normally be addressed during engine certification. Also, since the rain ingestion requirements in part 33 were not added until Amendment 33-6, the airplane applicant needs to evaluate the engine's certification basis to determine if the engine has been subjected to part 33 rain ingestion testing. If the engine does not have Amendment 33-6 or a subsequent amendment as part of the certification basis, in accordance with § 23.903(a)(2)(iii), the engine must have a safe service history of rain ingestion in similar installations.

Although testing is typically performed, if design analysis shows that the installation will not affect the water ingestion characteristics, appropriately substantiated design analysis may be adequate to demonstrate rain ingestion compliance. Proof could include, or be a combination of, items such as data from rig tests, previous tests by the applicant on a similar installation, service experience by the applicant on a similar installation, or representative developmental tests, and so forth.

If it is determined that testing for rain ingestion is required, flight test is not required. The intent of the part 23 rule is to ensure that the engine installation has the same rain ingestion tolerance as the certificated engine. Since a ground static engine test normally demonstrates engine certification compliance, use of installation ground tests at the required power/thrust settings has been the normally accepted means of compliance. You can use design analysis to determine critical configurations and conditions of the installation; possibly reducing required installation tests to those critical configurations and conditions instead of repeating the entire part 33 test conditions. Engine certification should address the results of the critical point analysis for the engine with the scope of required installation testing possibly influenced by this analysis. Therefore, it is important for the engine installer to research the conditions and requirements used for engine certification.

Other Considerations for Compliance

Amendment 23-53 also added requirements for ice, hail, and birds. Examples of installation issues normally not addressed by engine certification, Start Printed Page 53340but which should be addressed for installation compliance, include the following: Ice build-up on areas where ice shed may be ingested by the engines (for example, ice shed from wings into aft mounted engines) and consideration of items such as inlet splitters, acoustic liners, and so forth, that may be damaged by impact with ice, hail, and birds.

Start Signature

Issued in Kansas City, Missouri on August 16, 2000.

Michael Gallagher,

Manager, Small Airplane Directorate, Aircraft Certification Service.

End Signature End Supplemental Information

[FR Doc. 00-22541 Filed 8-31-00; 8:45 am]