What’s in a name?
There are many rumors as to how the magnetic compass, found in the cockpit of many aircraft, became known as the ‘whiskey compass.’ Some say it was dubbed the whiskey compass to remind pilots to refill the compass fluids with the alcoholic beverage instead of water due to its lower freezing temperature. Others say since the compass is also known as a ‘wet compass’ and with whiskey being the phonetic pilot-alphabet for ‘w,’ it then became the whiskey (‘w’) compass. Others claim that the US Navy would use whiskey in their compasses, up until sailors started drinking it due to their dry ship rule. Regardless of the origin of the nomenclature for the whiskey compass, CTS is bringing you some myth-busting facts about the compass and proper care techniques for the device.
Bubbles are bad for the device: Fact
Generally, these compasses are made to not have a bubble in them. If you see a bubble, most likely there is a leak somewhere in the device. Bubbles can cause a number of issues with the equipment, so it is recommended to immediately get it looked at.
I can fill the compass with any liquid that has a low freezing temperature: Fiction
There are two types of liquid compasses: alcohol-water based and oil based. If you use the wrong liquid for your model, you can ruin the device. For example, when you put water in the oil based compass, it will rust the magnets and discolor the card in the magnet. There is also a risk of adding too much water to the alcohol-water based compass, causing the device contents to freeze in certain temperatures. It is required to always have a professional, such as an instrument repair shop or an aviation maintenance technician refill the compass.
Swinging the compass is important to avoid deviation: Fact
Only maintenance technicians or repair shops can perform this action, and swinging the compass must be completed “whenever any ferrous component of the system (i.e. flux valve compensator, or Standby Compass) is installed, removed, repaired, or a new compass is installed” (AC 43.13-1B, Chapter 12, Section 3. Ground Operational Checks for Avionics Equipment (Non Electrical), Paragraph 12-37 Compass Swing). To properly swing the compass, you must align the aircraft on each magnetic heading of the series of lines marked along the taxiway or ramp, the compass rose, at the airport and adjust the compensating magnets to minimize the difference between the indicator and actual magnetic heading. Lines that are oriented to magnetic north are painted every 30°. Any error or deviation should be recorded on a compass correction card.
Note: Deviations can be caused by magnetic interference and swinging the compass will help reduce this error, but will not completely eliminate it. Remember to determine your magnetic course and then determine your compass course from your correction card.
The Whiskey or Magnetic Compass in the cockpit is arguably one of the most vital devices on the instrument panel, especially if/when other navigational tools are down. It’s important to keep the device full of the proper liquid and to ensure proper maintenance is kept for the device. Always consult an aviation maintenance technician or other expert before fixing or removing any part of the compass.