715
Federal Aviation Administration, DOT
§ 33.68
applicant must account for in-flight
ram effects in any critical point anal-
ysis or test demonstration of these
flight conditions.
(b) Operate throughout its flight
power range, including minimum de-
scent idle rotor speeds achievable in
flight, in the icing conditions defined
for turbojet, turbofan, and turboprop
engines in Appendices C and O of part
25 of this chapter, and for turboshaft
engines in Appendix C of part 29 of this
chapter. In addition:
(1) It must be shown through Critical
Point Analysis (CPA) that the com-
plete ice envelope has been analyzed,
and that the most critical points must
be demonstrated by engine test, anal-
ysis, or a combination of the two to op-
erate acceptably. Extended flight in
critical flight conditions such as hold,
descent, approach, climb, and cruise,
must be addressed, for the ice condi-
tions defined in these appendices.
(2) It must be shown by engine test,
analysis, or a combination of the two
that the engine can operate acceptably
for the following durations:
(i) At engine powers that can sustain
level flight: A duration that achieves
repetitive, stabilized operation for tur-
bojet, turbofan, and turboprop engines
in the icing conditions defined in Ap-
pendices C and O of part 25 of this
chapter, and for turboshaft engines in
the icing conditions defined in Appen-
dix C of part 29 of this chapter.
(ii) At engine power below that which
can sustain level flight:
(A) Demonstration in altitude flight
simulation test facility: A duration of
10 minutes consistent with a simulated
flight descent of 10,000 ft (3 km) in alti-
tude while operating in Continuous
Maximum icing conditions defined in
Appendix C of part 25 of this chapter
for turbojet, turbofan, and turboprop
engines, and for turboshaft engines in
the icing conditions defined in Appen-
dix C of part 29 of this chapter, plus 40
percent liquid water content margin,
at the critical level of airspeed and air
temperature; or
(B) Demonstration in ground test fa-
cility: A duration of 3 cycles of alter-
nating icing exposure corresponding to
the liquid water content levels and
standard cloud lengths starting in
Intermittent Maximum and then in
Continuous Maximum icing conditions
defined in Appendix C of part 25 of this
chapter for turbojet, turbofan, and tur-
boprop engines, and for turboshaft en-
gines in the icing conditions defined in
Appendix C of part 29 of this chapter,
at the critical level of air temperature.
(c) In addition to complying with
paragraph (b) of this section, the fol-
lowing conditions shown in Table 1 of
this section unless replaced by similar
CPA test conditions that are more crit-
ical or produce an equivalent level of
severity, must be demonstrated by an
engine test:
T
ABLE
1—C
ONDITIONS
T
HAT
M
UST
B
E
D
EMONSTRATED BY AN
E
NGINE
T
EST
Condition
Total air temperature
Supercooled water
concentrations
(minimum)
Median volume drop diameter
Duration
1. Glaze ice condi-
tions.
21 to 25
°
F (
¥
6 to
¥
4
°
C).
2 g/m
3
........................
25 to 35 microns ...................
(a) 10-minutes for
power below sus-
tainable level flight
(idle descent).
(b) Must show repet-
itive, stabilized op-
eration for higher
powers (50%, 75%,
100%MC).
2. Rime ice conditions
¥
10 to 0
°
F (
¥
23 to
¥
18
°
C).
1 g/m
3
........................
15 to 25 microns ...................
(a) 10-minutes for
power below sus-
tainable level flight
(idle descent).
(b) Must show repet-
itive, stabilized op-
eration for higher
powers (50%, 75%,
100%MC).
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