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Gremline Flight Safety Report: Carburettor Icing Alert System

the online flight safety digest

Text Box: carburettor icing alert

the gremline digest —  carburettor icing alert system

Carburettor Icing Alert System

Carburettor icing is very old problem that has caused many incidents and accidents over the years. It is possible to overcome the problem at the aircraft engine design stage but the majority of piston engines installed in general aviation aircraft using avgas or mogas were not designed to eliminate the hazard of carburettor icing. This leaves recreational pilots with the problem of understanding when carburettor icing is likely to occur and the need to understand the phenomenon and the actions necessary to avoid it. Our July 2008 article deals in detail with the mechanisms of carb icing, how to anticipate it, and how to deal with it; but the time is long overdue for a simple and affordable resolution that can be retro-fitted to aircraft where icing is a potential hazard.


There have been attempts to provide a modification to carburettors fitted to aero engines but these have not been totally successful. The UK Civil Aviation Authority (CAA) requires all such modifications to be “approved” before they are installed. The approval process costs time and money. An approved system that involves modification to the carburettor costs many hundreds of dollars to purchase and many more to install but is reputed to be less than 100% reliable.

      I decided to look at the problem from a slightly different viewpoint and try to develop a cheap, simple and reliable electronic warning system that would provide the pilot with a visual alert whenever the aircraft encountered conditions conducive to the formation of carburettor icing. A prototype was produced and passed to a friend to try it out in the air. It works. A world-wide patent search (costing £485) revealed that the design concept is original and has not been used previously.

     The prototype needs to be developed and improved so that it warns the pilot in a simple manner whenever the aircraft in is one of the four stages of carburettor icing illustrated on the classic carb icing chart as published in many flight safety articles and accident investigation reports. The present model provides two digital readouts that need to be interpreted by the pilot. The developed model will have four LCD lights, (coloured green, blue, orange and red to match the carb icing graph) that will flash whenever the aircraft encounters conditions conducive to the four different levels of carburettor icing. These warning will alert the pilot to the need to apply carburettor heating before there is any deterioration in the engine power and before the icing becomes established in the carburettor.

     This system does not require any modification to the aircraft engine or to the carburettor. It is self-contained and the small mobile phone sized instrument can be mounted in any convenient position within the flight instrument scan. The prototype cost a total of £25 including VAT. The modified production model is unlikely to cost very much more, and even if it cost twice as much it would still be much cheaper then a bent aircraft.

     The prototype was test flown by a friend in the CAA who is enthusiastic about its performance and its simplicity. The AAIB are enthusiastic about the idea but have not yet seen the instrument. A well-known UK supplier of aviation electronic devices has expressed an interest in marketing the developed instrument.

     I am not going to become a millionaire with this instrument and really cannot afford the time or money required to develop and market it. I would like to pass the project on to someone for development and marketing. I do believe it will enhance the safety of general aviation.




John Stewart-Smith

Managing Editor, Gremline

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Tel (UK): +44 (0)1348 831882


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