Operating Instructions - CPA2501
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Air Data Test Indicator
CPA2501
3 General Description
The CPA2501 can be a single channel altitude/altitude rate indicator (Ps only), a single channel airspeed/
airspeed rate indicator (Qc only) or it can be a dual channel unit configured with a Ps channel and Pt
channel or a Ps channel and a Qc channel. In the Ps/Pt version, Qc is calculated using the equation Qc
= Pt - Ps and is displayed in a “virtual” channel. In the Ps/Qc version, Pt is also calculated using the same
equation and is displayed in a “virtual” channel. Pressure in each channel can also be read in standard
pressure units. An optional barometer can also be installed and displayed as a channel.
Figure 3.1 - Desk top version
3.1 Definitions
Static Pressure (Ps): The absolute pressure of still air surrounding a body. Ps is pressure that would
have existed in the aircraft’s location if the aircraft had created no pressure disturbances; the atmospheric
pressure. Ps is proportional to altitude. The relationship between Ps and Altitude is non-linear.
Total Pressure (Pt): The sum of the local atmospheric pressure plus impact pressure created by the
aircraft moving through the atmosphere.
Impact Pressure (Qc): The pressure a moving stream of air produces against a surface which brings
part of the moving stream to rest. It is the difference between the Total and Static Pressures (Qc = Pt
- Ps). Qc is proportional to the aircraft speed relative to the surrounding air (indicated airspeed). The
relationship between Qc and indicated airspeed is non linear.
Qc = Pt - Ps
3.2 Features
Significant features designed into the CPA2501:
• A removable, highly stable, temperature compensated air data transducer package with Ps/Qc or Ps/
Pt configuration.
• Variant configuration: Single Ps Channel, or Single Qc Channel
• 7” Color LCD with touch screen
