What exactly is Precipitation Static?

Recently a received a question that I thought I would know but as it turns out – I did not.  As many of you may know, the last communication between the Hawaii Clipper and a PAA radio control station in located in the Philippines ended with the term “Rain Static”.  So what does that mean exactly and how does it matter to the mystery of the Hawaii Clipper?


In 1938,  it was documented by the FBI investigation that the final entry on the Clippers’ Radio Log was a “matter-of-fact report of position, altitude, speed, weather observation…” which led the agents and Pan Am officials “to believe the disaster – if there was one – came without warning.”  Further more “Pan Am crews and officials pointed out, have strict orders to instantly report any mechanical trouble, leading them to believe the operator would have shouted a few hasty words into his wireless telephone had engine or structural failure brought the aircraft down”.


In the November 25th, 1938 CAA Report on page 2 states that 0400 GCT position report was filed at 0403 by Captain Terletzky and completed at 0411.  As soon as the transmission was completed, the ground operator advised he had a weather sequence to transmit.  The aircraft advised that he was experiencing rain static and to wait.


The ground operator waited for one minute and tried to contact the Hawaii Clipper but she never responded.  An attempt was made to use the Direction Finder but no signal could be heard from the aircraft.  Incidentally, a A radio direction finder (RDF) is a device for finding the direction, or bearing, to a radio source. The act of measuring the direction is known as radio direction finding or sometimes simply direction finding (DF).


Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately, using two or more measurements of known transmitters, the location of a vehicle can be determined. RDF is widely used as a radio navigation system, especially with boats and aircraft.

At the time of loss of contact, the Hawaii Clipper was at an altitude of 9,200 feet with solid layer of stratocumulus clouds above and solid cumulus below with moderately rough air and experiencing some rain.  When the USAT Meigs arrived at the last point of communication a few hours later it reported smooth sea conditions, light winds and good visibility.  Was the aircraft really where it said it was or headed in another direction?

Precipitation (Rain) Static.

  1. Precipitation static (P-static) is caused by aircraft in flight coming in contact with uncharged particles. These particles can be rain, snow, fog, sleet, hail, volcanic ash, dust and any solid or liquid particles.
    1. When the aircraft strikes these neutral particles the positive element of the particle is reflected away from the aircraft and the negative particle adheres to the skin of the aircraft. In a very short period of time, a substantial negative charge will develop on the skin of the aircraft.
    2. If the aircraft is not equipped with static dischargers, or has an ineffective static discharger system, when a sufficient negative voltage level is reached, the aircraft may go into “CORONA.” That is, it will discharge the static electricity from the extremities of the aircraft, such as the wing tips, horizontal stabilizer, vertical stabilizer, antenna, propeller tips, etc.
    3. This discharge of static electricity can cause certain radio frequencies to become unreliable.


2 Comments Add yours

  1. David Wilma says:

    It would be interesting to know the solar-terrestrial data for that night. Were other stations in the western Pacific able to communicate with one another with or without difficulty. In 1938 there was an imperfect understanding of how the sun affected radio transmissions. Some bands are wide open and some are impossible. Obviously Manila was in touch with PAA 229, but how well?


  2. Guy says:

    A VERY good idea David. Thanks!


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