The aircraft run-up and equipment power-on time directly contribute to PAPR performance. Powering on ADS-B and other avionics immediately after engine start/engine checks will ensure optimal performance. The two devices most impacted by startup time are the skyBeacon GPS and the aircraft’s pre-existing altitude encoder. We recommend the avionics in the aircraft are given 4-5 minutes of warm-up time prior to departure.
Certified aviation GPS units require more time to acquire a high-integrity fix than the consumer GPS units. NIC failures from 0.5% to 5% have been traced to very short startup times. We recommend the skyBeacon be powered up immediately after engine start and allowed 5 minutes prior to takeoff.
This aircraft did not have sufficient run-up and the GPS was reporting a low integrity value.
We’ve tested several popular altitude encoders and recorded their startup times. Many are temperature corrected and may not provide valid altitude to the transponder for up to 5 minutes depending on the model and ambient temperature. Taking off without valid altitude data to the Mode C transponder does not meet the requirements of 91.227. In many cases, the pilot has no visual indication the encoder has reached operating temperature. Waiting a few minutes is a good best practice.