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Why Not Egg Timers?

Egg timers have been the state-of-the-art method of ensuring aircraft separation at many facilities and have been the fallback system where old-school electronic timers have failed and cannot be economically repaired.

Egg timers are cheap and reliable. So why aren't they an adequate solution for aircraft takeoff separations?

  • The Recat order requires 2, 3, 4, and 5 minute periods, with 4 1/2 and 5 1/2 minute periods required in rare cases. It's simply not practical to manage 4 periods with egg timers. 
  • Detecting the end of the timed period requires careful observation of the egg timer. There is no "end of period" signal when the last grain of sand falls. Watching the timer to determine when the last grain of sand has fallen distracts the controller from the important business at hand 
  • The purpose of the RECAT order is to increase throughput of airports while  ensuring flight safety. Accurate timing is essential to achieve the desired goals of the order. While egg timers may be accurate, delays may be encountered when the last grain of sand falling isn't immediately noticed. 
The WTT4/WTT5 timers solve these problems. The desired countdown period is easily initiated with a single button press. The selected period is indicated by an illuminated switch and the remaining time of the countdown period is shown by large bright 7-segment LED displays. The end of the countdown period is indicated by a distinctive tone and a flashing LED display.

The picture below shows a non-functional AWTT-3 wake turbulence timer and the fall-back egg timers used instead at Paine Field.

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