Yak 18T Flight Operations Manual
Page 78 of 82
Disclaimer: This manual is to be used as a reference only, it is based on translated Yak 18T Flight Operations
Manuals and has not been approved by the Yakovlev Design Bureau or any other authority.
airfield pressure with that one reported in the previous weather information. While
approaching, the height keeping control is carried out by the radio altimeter
After Landing
Before taxiing, switch the heating of the pitot-static tube off (if it was turned on).
12.2.6
Operational Limitations
1.
A permissible discrepancy between the barometric and atmospheric pressure scale
indications at the airfield level for the altimeter is 1.5mm of Hg. Do not match the
altimeter scales directly on the aircraft
2.
Time of the heating element continuous operation of the pitot static tube on the ground
is not more than 1.5m
Failures in the pitot and static pressure feed systems and actions of pilot in case of these
failures
1.
Clogging or icing of the static-pressure pick-up (static vents). This trouble, providing air-
tightness of the static pipe line is proper, is isolated by the following signs –
•
the variometer pointer is set to the zero position and does not change with variation
of the flight altitude
•
the altimeter does not change its readings with variation of the flight altitude
•
the speed indicator at climb will provide too low readings, and too high during at
descent
Pilot Actions
If the altimeter, speed indicator and variometer turn out to be detective, the pilot must
deliver a radio message to ATC, abort the task execution and take the course to the landing
airfield by indications of the gyro-horizon and the radio altimeter.
The flight speed is controlled by the engine power settings (by readings of the pressure and
vacuum gauge and tachometer).
2.
Clogging or icing of the pitot tube.
The main reason of the inlet port choking of the pitot-and-static tube is icing of the tube
nose, which can occur as a result of the heating element failure or if the latter was not
switched on. In case of pitot-and-static tube icing, clogging of its inlet port can take place
and drain orifices remain open. In this case, in the pitot-pressure chamber the pressure
equal to the atmospheric one is being set and the pitot tube becomes the static-pressure
pick-up. If the inlet port of the pitot-static tube and its drain orifices get clogged, this is
detected by the following signs –
•
the speed indicator maintains steady-state readings and does not respond to the
speed variation during the horizontal flight
•
while climbing, the speed indicator readings will be increased and will decrease
during descent
Actions of the pilot
Check whether the heating element of the pitot-static tube is switched on (the circuit breaker
HEATING CLOCK, must be turned on). If in 2-3 minutes after the pitot-static tube heating has
been switched on, the speed indicator readings are not restored, the pilot must inform ATC
and terminate the flight and take the appropriate course towards the landing airfield. Check
the flight speed from readings of the variometer and power settings of the engine using
indications of the vacuum gauge and tachometer.
Summary of Contents for 18T
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