[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR33.78]

[Page 775-776]
 
                     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

[[Page 776]]

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 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]