725 

Federal Aviation Administration, DOT 

§ 33.79 

hail, as defined in appendix B to this 
part. Acceptable engine operation pre-
cludes 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 alter-

native to the requirements specified in 
paragraph (a)(2) of this section, for 
rotorcraft turbine engines only, it 
must be shown that each engine is ca-
pable 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 dis-
tribution at the inlet plane, of at least 
four percent. Acceptable engine oper-
ation precludes flameout, run down, 
continued or non-recoverable surge or 
stall, or loss of acceleration and decel-
eration capability. It must also be 
shown after the ingestion that there is 
no unacceptable mechanical damage, 
unacceptable power loss, or other ad-
verse engine anomalies. The rain inges-
tion 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 oper-
ation, 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 sepa-
rate test for supersonic airplane en-
gines 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 en-
gine 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 millime-

ters) at 60,000 feet (18,000 meters) using 
the diameter corresponding to the low-
est 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 condi-
tions. 

(d) For an engine that incorporates 

or requires the use of a protection de-
vice, demonstration of the rain and 
hail ingestion capabilities of the en-
gine, 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 con-

stituents are of a size that will not 
pass through the protection device; 

(2) The protection device will with-

stand the impact of the subject rain 
and hail constituents; and 

(3) The subject of rain and hail con-

stituents, stopped by the protection de-
vice, will not obstruct the flow of in-
duction air into the engine, resulting 
in damage, power or thrust loss, or 
other adverse engine anomalies in ex-
cess of what would be accepted in para-
graphs (a), (b), and (c) of this section. 

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

§ 33.79

Fuel burning thrust augmentor. 

Each fuel burning thrust augmentor, 

including the nozzle, must— 

(a) Provide cutoff of the fuel burning 

thrust augmentor; 

(b) Permit on-off cycling; 
(c) Be controllable within the in-

tended range of operation; 

(d) Upon a failure or malfunction of 

augmentor combustion, not cause the 
engine to lose thrust other than that 
provided by the augmentor; and 

(e) Have controls that function com-

patibly with the other engine controls 
and automatically shut off augmentor 
fuel flow if the engine rotor speed drops 
below the minimum rotational speed at 

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