Narrative:

While finishing the transponder operational checkout procedure the manual states to close all the probe heater breakers and to shut off electrical power to the aircraft which coincided with the beginning of the afternoon scheduled break. Upon returning from break the aircraft power was reapplied to verify several non-thermal circuit breakers were not in a 'locked' state and after 5-10 minutes noticed the #1 airdata and standby airdata information on their respective displays depicting an uncommanded steep decline in airspeed and altitude. After 20-30 seconds of this aircraft power was shut down and it was later discovered that all the airdata probes heated with no notice or warning. After evaluation; it was found the two probe test adapters and the two aircraft airdata probes were damaged and needed repaired/replaced.it was discovered after the incident that in the aircraft maintenance manual in chapter 12 there is a procedure to configure the aircraft for maintenance. Among the many items listed there is a warning which states that all probe heater circuit breakers should be pulled and collared; failure to do so could result in uncommanded heating that could result in injury and damage to the aircraft. I would suggest that the chapter 12 configuration of the aircraft for maintenance be accomplished at all times this type of aircraft is in for a maintenance event at our hangar. I would also like to suggest the aircraft manufacturer amend their maintenance manual to make technicians performing maintenance on the airdata system or the activation of the weight on/off wheels procedures be directed to the chapter 12 warning of the heater probes. I feel that one of these two actions could have prevented the mishap which we experienced.

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Original NASA ASRS Text

Title: A Maintenance Technician working on a Global 5000 reported that after accomplishing some operational checkouts and resetting some circuit breakers the air data probes heated and two probe test adapters and the two aircraft air data probes were damaged.

Narrative: While finishing the Transponder Operational Checkout procedure the manual states to close all the probe heater breakers and to shut off electrical power to the aircraft which coincided with the beginning of the afternoon scheduled break. Upon returning from break the aircraft power was reapplied to verify several non-thermal circuit breakers were not in a 'locked' state and after 5-10 minutes noticed the #1 airdata and standby airdata information on their respective displays depicting an uncommanded steep decline in airspeed and altitude. After 20-30 seconds of this aircraft power was shut down and it was later discovered that all the airdata probes heated with no notice or warning. After evaluation; it was found the two probe test adapters and the two aircraft airdata probes were damaged and needed repaired/replaced.It was discovered after the incident that in the Aircraft Maintenance Manual in Chapter 12 there is a procedure to configure the aircraft for maintenance. Among the many items listed there is a warning which states that all probe heater circuit breakers should be pulled and collared; failure to do so could result in uncommanded heating that could result in injury and damage to the aircraft. I would suggest that the Chapter 12 Configuration of the Aircraft for Maintenance be accomplished AT ALL TIMES this type of aircraft is in for a maintenance event at our hangar. I would also like to suggest the aircraft manufacturer amend their maintenance manual to make technicians performing maintenance on the airdata system OR the activation of the weight on/off wheels procedures be directed to the Chapter 12 warning of the heater probes. I feel that one of these two actions could have prevented the mishap which we experienced.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.