726 

14 CFR Ch. I (1–1–24 Edition) 

§ 33.78 

T

ABLE

1—M

INIMUM

I

CE

S

LAB

D

IMENSIONS

B

ASED ON

E

NGINE

I

NLET

S

IZE

 

Engine Inlet Hilite area 

(sq. inch) 

Thickness 

(inch) 

Width 
(inch) 

Length 

(inch) 

0 .......................................................................................................................

0 .25 0 

3.6 

80 .....................................................................................................................

0 .25 6 

3.6 

300 ...................................................................................................................

0 .25 12 3.6 

700 ...................................................................................................................

0 .25 12 4.8 

2800 .................................................................................................................

0 .35 12 8.5 

5000 .................................................................................................................

0 .43 12 

11.0 

7000 .................................................................................................................

0 .50 12 

12.7 

7900 .................................................................................................................

0 .50 12 

13.4 

9500 .................................................................................................................

0 .50 12 

14.6 

11300 ...............................................................................................................

0 .50 12 

15.9 

13300 ...............................................................................................................

0 .50 12 

17.1 

16500 ...............................................................................................................

0 .5 12 

18.9 

20000 ...............................................................................................................

0 .5 12 

20.0 

[Doc. No. 16919, 49 FR 6852, Feb. 23, 1984, as 
amended by Amdt. 33–19, 63 FR 14798, Mar. 26, 
1998; 63 FR 53278, Oct. 5, 1998; Amdt. 33–20, 65 
FR 55856, Sept. 14, 2000; Amdt. 33–34, 79 FR 
65537, Nov. 4, 2014] 

§ 33.78

Rain and hail ingestion. 

(a) 

All engines. (1) The ingestion of 

large hailstones (0.8 to 0.9 specific grav-
ity) at the maximum true air speed, up 
to 15,000 feet (4,500 meters), associated 
with a representative aircraft oper-
ating 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 en-
gine 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 simu-
late a hailstone encounter and the 
number and size of the hailstones shall 
be determined as follows: 

(i) One 1-inch (25 millimeters) diame-

ter hailstone for engines with inlet 
areas of not more than 100 square 
inches (0.0645 square meters). 

(ii) One 1-inch (25 millimeters) di-

ameter 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 ex-
cept as provided in paragraph (b) of 
this section, it must be shown that 
each engine is capable of acceptable op-
eration throughout its specified oper-

ating envelope when subjected to sud-
den encounters with the certification 
standard concentrations of rain and 
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 

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727 

Federal Aviation Administration, DOT 

§ 33.83 

(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 
which the augmentor is intended to 
function. 

[Amdt. 33–6, 39 FR 35468, Oct. 1, 1974] 

Subpart F—Block Tests; Turbine 

Aircraft Engines 

§ 33.81

Applicability. 

This subpart prescribes the block 

tests and inspections for turbine en-
gines. 

[Doc. No. 3025, 29 FR 7453, June 10, 1964, as 
amended by Amdt. 33–6, 39 FR 35468, Oct. 1, 
1974] 

§ 33.82

General. 

Before each endurance test required 

by this subpart, the adjustment setting 
and functioning characteristic of each 
component having an adjustment set-
ting and a functioning characteristic 
that can be established independent of 
installation on the engine must be es-
tablished and recorded. 

[Amdt. 36–6, 39 FR 35468, Oct. 1, 1974] 

§ 33.83

Vibration test. 

(a) Each engine must undergo vibra-

tion surveys to establish that the vi-
bration characteristics of those compo-
nents that may be subject to mechani-
cally or aerodynamically induced vi-
bratory excitations are acceptable 
throughout the declared flight enve-
lope. The engine surveys shall be based 
upon an appropriate combination of ex-
perience, analysis, and component test 
and shall address, as a minimum, 
blades, vanes, rotor discs, spacers, and 
rotor shafts. 

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