Blog 3.2 Air Data

 The Lockheed C-130 Hercules, uses a pitot static system to collect air data. The information from this system is used to determine barometric altitude, airspeed, and vertical speed. The pitot tubes measure ram air from the relative wind and the static ports measure the ambient air pressure.

Pitot tubes with and without covers. Covers prevent damage and FOD from entering on the ground.

Static port for measuring ambient air pressure.

     There are two separate, identical, and redundant systems, each one feeds to its own air data computer and then to the pilot or the co-pilot. On the C-130 J model the first indication of a problem with any system is usually the Alerts, Cautions, and Warning System (ACAWS) announcement. This may include an audible signal as well as a digital phrase stating the problem on one of the pilot's screens.

ACAWS messages area.

      One problem which may arise is an airspeed split. When the pilot and co-pilot's tachometers show different air speeds. This can be cause by a blockage of a pitot tube, usually by ice, a malfunction in the air data computer, or a leak in the air data system among other potential problems.

A Pitot-Static tube similar to the C-130. Note the static holes on the tube itself.

     Without accurate air data the pilots will be unable to make safe decisions regarding stall speeds, landing and takeoff speeds and overspeed limits for various airplane configurations. Further it is unsafe to assume that the broken system is the slow system as many aircraft systems, especially the C-130 are computer controlled and so the cause of the problem may not be deduced in flight.

Druck brand test set. This machine produces pressure and vacuum to simulate flight.

    If this occurs in flight it is best to use the "slower" altimeter for all slow speed and stall speed limits and to use the "faster" altimeter for all overspeed limits. Once on the ground the issue will need to be immediately addressed. This involves setting up an air data test set hooked up to the pitot tubes and static ports and simulates an aircraft in flight. Using this data the system the maintainers can then troubleshoot to determine the faulty component.

This fitting goes over the pitot tube. Hoses run from it to the test set.

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ERAUSpecialVFR. (2017, August 01). Pitot-Static Instruments. Retrieved December 19, 2020, from                    https://www.youtube.com/watch?v=kdFGbUouE_4

United States, Coast Guard. (n.d.). Flight Manual C-130 J USCG Series Aircraft.