Refer to figure.
Indicated Airspeed (IAS) is a function of the difference between:
- the Total Pressure (Pt) measured by a forward facing pitot head or probe and;
- the Ambient or Static Pressure (Ps) measured at static plates or ports.
Complete or partial blockages of pitot heads and static ports can confuse an unprepared crew and may be caused by:
- In-Flight Icing
- Volcanic Ash
- Heavy rain
- Crude Oil Smoke
- Failure to remove maintenance seals or protective covers from external vents prior to flight
- Failure to select pitot static heat on
- Damage to the radome/nose cone of an aircraft causing erroneous pitot and static information.
Flight crews should monitor the primary flight path parameters (pitch attitude, thrust setting and indicated airspeed) during periods of potential icing encounters.
Some systems include an Airspeed Disagree Alert (figure)
Airspeed Disagree Alert (amber) - Indicates the Captain’s and F/O’s airspeed indications disagree by more than 5
knots for 5 continuous seconds.
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