Precipitation Static Precipitation static, often referred to as P-static, occurs  when accumulated static electricity is discharged from the  extremities of the aircraft. This discharge has the potential  to create problems for the instrument pilot. These problems  range from the serious, such as erroneous magnetic compass  readings and the complete loss of very high frequency (VHF)  communications to the annoyance of high-pitched audio  squealing and St. Elmo’s fire.  [Figure 11-1] Precipitation static is caused when an aircraft encounters  airborne particles during flight (e.g., rain or snow) and  develops a negative charge. It can also result from  atmospheric electric fields in thunderstorm clouds. When  a significant negative voltage level is reached, the aircraft  discharges it, which can create electrical disturbances. This  electrical discharge builds with time as the aircraft flies in  precipitation. It is usually encountered in rain, but snow can  cause the same effect. As the static buildup increases, the  effectiveness of both communication and navigation systems  decreases to the point of potential unusability.  To reduce the problems associated with P-static, the pilot  should ensure the aircraft’s static wicks are properly maintained  and accounted for. Broken or missing static wicks should be  replaced before an instrument flight.  [Figure 11-2] Preventing aircraft system malfunctions that might lead  to an inflight emergency begins with a thorough preflight  Aircraft System Malfunctions Figure 11-2. One example of a static wick installed on aircraft  control surface to bleed off static charges built up during flight.  This prevents static buildup and St. Elmo’s fire by allowing the  static electricity to dissipate harmlessly. Figure 11-1.  St. Elmo’s Fire is harmless but may affect both communication and navigation radios, especially the lower frequencies  such as those used on the automatic direction finding (ADF). 11-3