DISCREPANCY - Pilot reports receiving an ADS-B 1 FAIL message during flight. No other discrepancies noted during the ADS-B Failure.

AIRCRAFT CONFIGURATION - Challenger 604 equipped with dual Transponder’s, Air Data Computer’s (ADC) and GPS’.

SYSTEM DESCRIPTIOIN - The Challenger 604 is equipped with dual redundant ADS-B systems. Each system consists of a Transponder, Air Data Computer and GPS. The GPS provides a WAAS GPS signal to the transponder via an ARINC 429 Bus, the transponder then reports that signal to the ADS-B ground stations and near by aircraft equipped with ADS-B In. The Air Data Computer also provides the transponder with Altitude and Air Speed via a ARINC 429 Bus, the transponder then provides the information to the ADS-B ground stations and near by aircraft equipped with ADS-B In.

TROUBLESHOOTING - The first step to diagnose this issue is inspecting the GPS and Transponder statuses on the MCDU. In this case GPS 1 continuously searched for satellite signal but never captured more than one satellite. The GPS continuously searches for satellites and is considered a good WAAS signal once 6 or more satellite’s are captured. Always assure aircraft is not in a hangar when troubleshooting a GPS, the GPS could possible be in working condition but GPS signal may be blocked by hangar.

Once GPS 1 was found to be failing an inspection of the GPS antenna coax cable and wire harness connector was performed. In this case the discrepancy was pretty obvious, the cable was disconnected at the TNC connector crimp. The original installer did not properly crimp the TNC connector to the coax cable also the pin was soldered instead of crimped causing the pin not to lock inside the TNC connector.

CORRECTIVE ACTION - A new TNC connector was crimped on to the antenna coax cable and cable was re-routed to reduce tension when connected. Operation test of the GPS and ADS-B system were performed with no issues noted. Aircraft has completed multiple flights with no further discrepancies reported.

TIPS TO DIAGNOSING AN ADS-B FAILURE -

1. If failure is reported by tower ask what information they are missing. ADS-B consists of multiple information like ALT, Air Speed, Identification, and Location. Knowing what information is missing you can then troubleshoot the correct system.

2. If you do not know what information is missing an ADS-B Performance Report of your last flight can be downloaded or previous flights. This may provide you with the missing information.

3. Check the status of your GPS and Altitude source. Each system setup is different but in most cases you can see the GPS and Altitude status’ on your GPS unit or Transponder. Missing GPS or Altitude have been the most common causes of ADS-B failures.

4. Always remember if work to the Transponder and Altitude reporting system is required (i.e. transponder removal and wiring checks) a test of that system must be performed in accordance with 91.411 and 91.413 by a certified repair station.