April 2000 Issue

Letters 4/00

AI Back-Ups
Your recent article on the various gyro back-up options was interesting, especially in light of recent accidents that were the apparent result of loss of vacuum. I agree that a second electric AI is probably the best bet, especially for single-engine aircraft. I think that the following points are sometimes overlooked when considering backup options for the vacuum pump or AI:

The vacuum pump is guaranteed to fail eventually, and should therefore be replaced periodically before it does. Perhaps every 500 hours.

If you’re going to install a second engine-driven vacuum pump, then dispense with the electric clutch arrangement and let the pump run full time, just l...

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