[Code of Federal Regulations]

[Title 14, Volume 1]

[Revised as of January 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 14CFR33.78]



[Page 784-785]

 

                     TITLE 14--AERONAUTICS AND SPACE

 

CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION

 

PART 33_AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES--Table of Contents

 

       Subpart E_Design and Construction; Turbine Aircraft Engines

 

Sec. 33.78  Rain and hail ingestion.



    (a) All engines. (1) The ingestion of large hailstones (0.8 to 0.9 

specific gravity) at the maximum true air speed, up to 15,000 feet 

(4,500 meters), associated with a representative aircraft operating in 

rough air, with the engine at maximum continuous power, may not cause 

unacceptable mechanical damage or unacceptable power or thrust loss 

after the ingestion, or require the engine to be shut down. One-half the 

number of hailstones shall be aimed randomly over the inlet face area 

and the other half aimed at the critical inlet face area. The hailstones 

shall be ingested in a rapid sequence to simulate a hailstone encounter 

and the number and size of the hailstones shall be determined as 

follows:

    (i) One 1-inch (25 millimeters) diameter hailstone for engines with 

inlet areas of not more than 100 square inches (0.0645 square meters).

    (ii) One 1-inch (25 millimeters) diameter and one 2-inch (50 

millimeters) diameter hailstone for each 150 square inches (0.0968 

square meters) of inlet area, or fraction thereof, for engines with 

inlet areas of more than 100 square inches (0.0645 square meters).

    (2) In addition to complying with paragraph (a)(1) of this section 

and except as provided in paragraph (b) of this section, it must be 

shown that each engine is capable of acceptable operation throughout its 

specified operating envelope when subjected to sudden encounters with 

the certification standard concentrations of rain and hail, as defined 

in appendix B to this part. Acceptable engine operation precludes 

flameout, run down, continued or non-recoverable surge or stall, or loss 

of acceleration and deceleration capability, during any three minute 

continuous period in rain and during any 30 second continuous period in 

hail. It must also be shown after the ingestion that there is no 

unacceptable mechanical damage, unacceptable power or thrust loss, or 

other adverse engine anomalies.

    (b) Engines for rotorcraft. As an alternative to the requirements 

specified in paragraph (a)(2) of this section, for rotorcraft turbine 

engines only, it must be shown that each engine is capable of acceptable 

operation during



[[Page 785]]



and after the ingestion of rain with an overall ratio of water droplet 

flow to airflow, by weight, with a uniform distribution at the inlet 

plane, of at least four percent. Acceptable engine operation precludes 

flameout, run down, continued or non-recoverable surge or stall, or loss 

of acceleration and deceleration capability. It must also be shown after 

the ingestion that there is no unacceptable mechanical damage, 

unacceptable power loss, or other adverse engine anomalies. The rain 

ingestion must occur under the following static ground level conditions:

    (1) A normal stabilization period at take-off power without rain 

ingestion, followed immediately by the suddenly commencing ingestion of 

rain for three minutes at takeoff power, then

    (2) Continuation of the rain ingestion during subsequent rapid 

deceleration to minimum idle, then

    (3) Continuation of the rain ingestion during three minutes at 

minimum idle power to be certified for flight operation, then

    (4) Continuation of the rain ingestion during subsequent rapid 

acceleration to takeoff power.

    (c) Engines for supersonic airplanes. In addition to complying with 

paragraphs (a)(1) and (a)(2) of this section, a separate test for 

supersonic airplane engines only, shall be conducted with three 

hailstones ingested at supersonic cruise velocity. These hailstones 

shall be aimed at the engine's critical face area, and their ingestion 

must not cause unacceptable mechanical damage or unacceptable power or 

thrust loss after the ingestion or require the engine to be shut down. 

The size of these hailstones shall be determined from the linear 

variation in diameter from 1-inch (25 millimeters) at 35,000 feet 

(10,500 meters) to \1/4\-inch (6 millimeters) at 60,000 feet (18,000 

meters) using the diameter corresponding to the lowest expected 

supersonic cruise altitude. Alternatively, three larger hailstones may 

be ingested at subsonic velocities such that the kinetic energy of these 

larger hailstones is equivalent to the applicable supersonic ingestion 

conditions.

    (d) For an engine that incorporates or requires the use of a 

protection device, demonstration of the rain and hail ingestion 

capabilities of the engine, as required in paragraphs (a), (b), and (c) 

of this section, may be waived wholly or in part by the Administrator if 

the applicant shows that:

    (1) The subject rain and hail constituents are of a size that will 

not pass through the protection device;

    (2) The protection device will withstand the impact of the subject 

rain and hail constituents; and

    (3) The subject of rain and hail constituents, stopped by the 

protection device, will not obstruct the flow of induction air into the 

engine, resulting in damage, power or thrust loss, or other adverse 

engine anomalies in excess of what would be accepted in paragraphs (a), 

(b), and (c) of this section.



[Doc. No. 28652, 63 FR 14799, Mar. 26, 1998]