Appendix 5.2 — Airworthiness Standards Aircraft Engines — FAR 33

Part 33.77 Foreign Object Ingestion

(a)  Ingestion of a 4-pound bird, under the conditions prescribed in paragraph (e) of this section, may not cause the engine to:

  1. Catch fire;
  2. Burst (release hazardous fragments through the engine case);
  3. Generate loads greater than those ultimate loads specified in Sec. 33.23(a); or
  4. Lose the capability of being shut down.

(b)  Ingestion of a 3-pound bird or 1.5-pound bird, under the conditions prescribed in paragraph (e) of this section, may not:

  1. Cause more than a sustained 25 percent power or thrust loss;
  2. Require the engine to be shut down within 5 minutes from the time of the ingestion; or
  3. Result in a potentially hazardous condition.

(c)  (relates to ice ingestion)

(d)  (relates to protective devices)

(e)  Compliance with paragraphs (a), (b), and (c) of this section must be shown by engine tests under the following conditions:

Foreign Object (BIRDS) Test Quantity Speed of Foreign Object Engine Operation Ingestion
3-ounce size One for each 50 square inches of inlet area or fraction thereof, up to a maximum of 16 birds. 3-ounce bird ingestion not required if a 1.5-pound bird will pass the inlet guide vanes into the rotor blades. Liftoff speed of typical aircraft. Takeoff In rapid sequence to simulate a flock encounter, and aimed at selected critical areas.
1.5-pound size One for the first 300 square inches of inlet area, if it can enter the inlet, plus one for each additional 600 square inches of inlet area, or fraction thereof, up to a maximum of eight birds. Initial climb speed of typical aircraft. Takeoff In rapid sequence to simulate a flock encounter, and at selected critical areas.
4-pound size One, if it can enter the inlet. Maximum climb speed of typical aircraft if the engine has inlet guide vanes. Liftoff speed of typical aircraft, if the engine does not have inlet guide vanes. Takeoff Aimed at critical area.

Part 23.903 Normal, Utility, Acrobatic, and Commuter Category Airplanes; and Part 25.903 Transport Category Airplanes

Both sections have identical wording as follows:

(2)  Each turbine must either:

  1. Comply with Secs. 33.77 and 33.78 of this chapter in effect on April 30, 1998; or as subsequently amended;
  2. Comply with Sec. 33.77 of this chapter in effect on October 31, 1974, or as subsequently amended prior to April 30, 1998, and must have a foreign object ingestion service history that has not resulted in any unsafe condition; or
  3. Be shown to have a foreign object ingestion service history in similar installation locations, which has not resulted in any unsafe condition.
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