TM 1-1520-238-10
5-2
Change 9
Section II.
SYSTEM LIMITS
5.5 INSTRUMENT OPERATING RANGES AND
MARKINGS.
5.5.1 Instrument Marking Color Code.
Operating lim-
itations and ranges (fig 5-1) are illustrated by colors on the
engine, flight, and utility system instruments. RED mark-
ings indicate the limit above or below which continued op-
eration is likely to cause damage or shorten component
life. YELLOW (light or dark) markings indicate the range
when special attention should be given to that operation
covered by the instrument. Operation is permissible in the
yellow range, but may be time limited or cautionary.
GREEN markings indicate the safe or normal range of op-
eration. Scales with green-coded, yellow-coded, or red-
coded segments above green-coded segments operate in
this manner; the segment will light in normal progression
and remain on as the received signal level increases.
Those segments will go off in normal progression as the
received signal level decreases. Scales with red-colored
and/or yellow-coded segments below green-coded seg-
ments operate in this manner; when the received signal
level is zero or bottom scale, the segments will light in nor-
mal progression and will remain on. When the first seg-
ment above the red or yellow range goes on, all red-coded
or yellow-coded segments will go off. These segments will
remain off until the received signal level indicates a read-
ing at or within the red or yellow range. At that time all red-
coded or yellow-coded segments will go on and the scale
display will either go on or off in normal progression, de-
pending upon the received signal level. Blue colored seg-
ments indicate that power is on.
5.5.2 Rotor Limitations.
It is not abnormal to observe
a % RPM 1 and 2 speed split during autorotational de-
scent when the engines are fully decoupled from the
transmission. A speed increase from 100% reference to
104% is possible. Refer to figure 5-1 for limitations.
a. Rotor Start and Stop Limits.
Maximum wind ve-
locity for rotor start or stop is 45 knots.
5.5.3 Engine and Rotor Instruments. The absolute limi-
tations, regardless of atmospheric conditions, are shown
in figure 5-1. For variations in power available with tem-
perature and pressure altitude, refer to charts in chapter 7
(
) or chapter 7A (
).
5.5.4 DECU/ECU Gauge Bias. The DECU (701C) incor-
porates a 71 C bias in its software which results in the in-
dicated TGT reading cooler than the actual TGT. This per-
mits use of the same TGT Gauge for the
and
engines.
NOTE
The Np and Nr triple tachometer for the
and
engines have different markings.
However, both engines should be operated
within the same normal operating limits of
104% Np and the maximum Nr limit of
110%.
