Policy Letter 161
Resetting Tripped Circuit Breakers
RDIMS No. 362923
Air operators shall develop training programs intended for crew members, maintenance personnel, and ground servicing personnel that clearly state company policies and procedures with regard to resetting tripped circuit breakers (CB). These policies and procedures should promote awareness of safety concerns associated with resetting tripped CBs and stress the importance of strict adherence to specific safety guidance by the manufacturer.
This policy applies to all air operators.
Sections 702.76, 703.98 and 704.115 of the Canadian Aviation Regulations (CARs);
Paragraph 705.124(1)(a) of the CARs, Flight Crew Members;
Paragraph 705.124(1)(b) of the CARs, All Crew Members.
Aircraft Training Programs:
Subsection 722.76(7) of the Commercial Air Service Standard (CASS), Ground Technical Type training;
Initial and Recurrent;
Subsection 722.76(12) of the CASS, Single-engine Aeroplanes Carrying Persons other than Flight Crew under Instrument Flight Rule (IFR) - Pilot Training Requirements, Required Synthetic Training Devices Exercises.
Aeroplane Training Programs:
Subsections 723.98(6), 724.115(7), and 725.124(6) of the CASS, Technical Ground Training - Initial and Recurrent;
Subsections 723.98(8), 724.115(9), and 725.124(9) of the CASS, Level A Training Program;
Subsections 723.98(9), 724.115(10), and 725.124(10) of the CASS, Level B Training Program;
Subsections 722.76(10), 723.98(10), 724.115(11), and 725.124(13) of the CASS, Aeroplane Flight Training Program;
Subsection 723.98(24) of the CASS, Single-engine Aeroplanes Carrying Passengers Visual Flight Rules (VFR) at Night or Under IFR (c) Required Synthetic Training Devices Exercises;
TP 12296 E Section 6.2A.7 of the CASS.
Helicopter Training Programs:
Subsections 723.98(6) and 724.115(7) of the CASS, Technical Ground Training - Initial and Recurrent;
Subsections 723.98(8) and 724.115(9) of the CASS, Level A Training Program;
Subsections 723.98(9) and 724.115(10) of the CASS, Level B Training Program;
Subsections 723.98(10) and 724.115(11) of the CASS, Helicopter Only Flight Training Program.
Aircraft Flight Manual (AFM)
Historically, crew members, maintenance personnel, and aircraft ground servicing personnel, (e.g., aircraft cleaners, aircraft fuelers, and baggage loading personnel) have viewed the resetting of a tripped CB as a relatively common occurrence in operations. Generally, resetting a tripped CB is met with no adverse results.
However, there are occasions where smoke, burned wires, electrical odors, arcing, and loss of related aircraft systems have been reported as a result of resetting tripped CBs. Aircraft manufacturers normally provide guidance in the AFM, MM, and aircraft servicing manuals that enables crew members, maintenance personnel, and aircraft ground servicing personnel to perform their tasks with a high degree of safety.
There is a widely held view that one reset of any tripped CB is acceptable. Locating and eliminating any associated fault is required prior to considering resetting any CB remembering that both high and low ampere CBs could readily ignite a fire.
Transport Canada provided information on this issue in the Aviation Safety Letter 1/2001 titled "The Deliberate Weak Link in the Electrical Chain" which clearly recommends that organizations develop and incorporate a comprehensive policy on CB. The Aeronautical Information Publication (AIP) Canada section AIR 4.11 Circuit Breakers and Alerting Devices also provides guidance on this subject.
Each air operator shall develop and implement policies and procedures for the resetting of tripped CBs and these requirements will form part of the air operator's training program requirements.
The AFM and MM procedures and limitations shall be the basis for the air operator's specific CB resetting procedures.
Subparts 702, 703, 704 and 705 of the CARs training programs requires that each flight crew member is knowledgeable with respect to aircraft systems operation and limitations as contained in the AFM, the aircraft operating manual and the SOPs when dealing with system malfunctions and failures including electrical systems. Paragraph 705.124(1)(b) of the CASS requires flight attendants to identify the function of a CB in electrical panels and describe the procedures for tripped CB including reset and crew communication procedures. They must also be able to describe the potential hazards to flight safety if CB procedures are not followed.
When considering the resetting of tripped CBs the procedures shall comply with the AFM, instructions from the original equipment manufacturer and any other official documents.
Company policies and procedures regarding resetting must be clearly stated and readily available to crew members. These policies and procedures should promote increased awareness of safety concerns associated with resetting tripped CBs and should stress the importance of strict adherence to specific safety guidance generated by the manufacturer.
General. There is a latent danger in resetting a CB tripped by an unknown cause because the tripped condition is a signal that something may be wrong in the related circuit. Until it is determined what has caused a trip to occur, crew members have no way of knowing the consequences of resetting a tripped CB.
CB Associated with Fuel Pump Circuit or Fuel Quantity Indicating System (FQIS). Special caution is appropriate where fuel pumps and/or FQIS are involved, because of the possibility that arcing might lead to the ignition of fuel or fuel vapors.
The resetting of fuel boost pump and/or the Fuel Quantity Indicator CBs in-flight is not recommended unless authorized by the aircraft manufacturer, and then only when authorized by the pilot-in-command.
The resetting of fuel boost pump and/or Fuel Quantity Indicator CBs on the ground, without first identifying the source of the electrical fault is not recommended.
On-the-Ground. A CB tripped by an unknown cause may only be reset on the ground after maintenance has determined the cause of the trip and has determined that the CB may be safely reset. A CB may be cycled (tripped, pulled or reset) where it is required to be performed within approved maintenance inspection criteria, or as part of an approved trouble-shooting procedure, unless doing so is specifically prohibited. If an air operator's minimum equipment list contains procedures that allow a tripped CB to be reset, then the same cautions with reference to resetting tripped CBs identified elsewhere in this Policy Letter also applies.
Resetting a CB tripped by an unknown cause should normally be a maintenance function conducted on the ground.
In-Flight. A tripped CB shall not be reset in flight unless doing so is consistent with explicit procedures specified in the approved operating manual, SOPs, checklists and AFM used by the crew members or unless, in the judgment of the pilot-in-command, resetting the CB is necessary for the safe completion of the flight. Crew members should limit resetting of CBs to one in-flight reset where this action is required.
No attempt should be made to reset a CB if it trips a second time.
Logbook Write-up. A detailed logbook write-up is a proven safety practice, and a maintenance control system is a requirement as per Section 706.05 of the CARs.
Defect Rectification and Control Procedures.
Section 706.05 of the CARs states "An air operator shall include in its maintenance control system the procedures referred to in the CASS for:
Defect Recording and Control.
Section 726.05 of the CASS states "(1) The defect recording system shall include a method to highlight defects that recur, so that they are readily identifiable by flight crews and the maintenance organization at all bases where the aircraft is operated. The air operator is responsible for identifying defects as recurring defects to maintenance personnel in order to avoid the duplication of unsuccessful attempts at rectification."
This write up is a proven safety practice for tracking and may provide maintenance personnel with the key to prompt trouble-shooting and effective corrective action on the ground. That write-up should include the following:
ACTION. The POI monitoring, reviewing and approving pertinent training programs in COMs and company documentation shall ensure that commercial air operators have incorporated CB resetting procedures provided by manufacturers into their manuals. The information must provide adequate detail for personnel to address resetting tripped CBs. Inspectors shall ensure that crew members training programs contain company policies and explicit procedures regarding the resetting of tripped CBs, both in-flight and on the ground. The procedures shown in the manuals used by the air operator's crew members, maintenance personnel, and aircraft ground servicing personnel shall be consistent with though not less restrictive than, the aircraft manufacturer's guidance and this Policy Letter.
This Policy Letter is designated AARX No. 161.
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