content_image/600622.jpg content_image/600621.jpg content_image/600620.jpg
<img src='content_image/600622.jpg'>

Attitude instrument flying in helicopters is essentially visual flying with the flight instruments substituted for the various reference points on the helicopter and the natural horizon. Control changes, required to produce a given attitude by reference to instruments, are identical to those used in helicopter VFR flight, and your thought processes are the same. Basic instrument train- ing is intended as a building block towards attaining an instrument rating. It will also enable you to do a 180° turn in case of inadvertent incursion into instrument meteorological conditions (IMC). 

## FLIGHT INSTRUMENTS 

When flying a helicopter with reference to the flight instruments, proper instrument interpretation is the basis for aircraft control. Your skill, in part, depends on your understanding of how a particular instrument or system functions, including its indications and limita- tions. With this knowledge, you can quickly determine what an instrument is telling you and translate that information into a control response. 

## PITOT-STATIC INSTRUMENTS 

The pitot-static instruments, which include the airspeed indicator, altimeter, and vertical speed indicator, oper- ate on the principle of differential air pressure. Pitot pressure, also called impact, ram, or dynamic pressure, is directed only to the airspeed indicator, while static pressure, or ambient pressure, is directed to all three instruments. An alternate static source may be included allowing you to select an alternate source of ambient pressure in the event the main port becomes blocked. [Figure 12-1] 

## AIRSPEED INDICATOR 

The airspeed indicator displays the speed of the heli- copter through the air by comparing ram air pressure from the pitot tube with static air pressure from the static port—the greater the differential, the greater the speed. The instrument displays the result of this pres- sure differential as indicated airspeed (IAS). Manufacturers use this speed as the basis for determin- ing helicopter performance, and it may be displayed in knots, miles per hour, or both. [Figure 12-2] When an indicated airspeed is given for a particular situation, you normally use that speed without making a correc- tion for altitude or temperature. The reason no correc- 

<img src='content_image/600621.jpg'>

tion is needed is that an airspeed indicator and aircraft performance are affected equally by changes in air den- sity. An indicated airspeed always yields the same performance because the indicator has, in fact, com- pensated for the change in the environment. 

<img src='content_image/600620.jpg'>

INSTRUMENT CHECK —During the preflight, ensure that the pitot tube, drain hole, and static ports are unob- structed. Before liftoff, make sure the airspeed indicator is reading zero. If there is a strong wind blowing directly at the helicopter, the airspeed indicator may read higher 

