Federal Aviation Administration, DOT

Section 33.68

applicant must account for in-flight
ram effects in any critical point analysis or test demonstration of these
flight conditions.
(b) Operate throughout its flight
power range, including minimum descent 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 complete ice envelope has been analyzed,
and that the most critical points must
be demonstrated by engine test, analysis, or a combination of the two to operate acceptably. Extended flight in
critical flight conditions such as hold,
descent, approach, climb, and cruise,
must be addressed, for the ice conditions 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 turbojet, turbofan, and turboprop engines
in the icing conditions defined in Appendices C and O of part 25 of this
chapter, and for turboshaft engines in
the icing conditions defined in Appendix 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 altitude 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 Appendix 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 facility: A duration of 3 cycles of alternating 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 turboprop engines, and for turboshaft engines 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 following conditions shown in Table 1 of
this section unless replaced by similar
CPA test conditions that are more critical or produce an equivalent level of
severity, must be demonstrated by an
engine test:

TABLE 1 - CONDITIONS THAT MUST BE DEMONSTRATED BY AN ENGINE TEST

spaschal on DSK3GDR082PROD with CFR

Condition

Total air temperature

Supercooled water
concentrations
(minimum)

Median volume drop diameter

Duration
(a) 10-minutes for
power below sustainable level flight
(idle descent).
(b) Must show repetitive, stabilized operation for higher
powers (50%, 75%,
100%MC).
(a) 10-minutes for
power below sustainable level flight
(idle descent).
(b) Must show repetitive, stabilized operation for higher
powers (50%, 75%,
100%MC).

1. Glaze ice conditions.

21 to 25 SectionF (Section6 to
Section4 SectionC).

2 g/m3 ........................

25 to 35 microns ...................

2. Rime ice conditions

Section10 to 0 SectionF (Section23 to
Section18 SectionC).

1 g/m3 ........................

15 to 25 microns ...................

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