Maintenance and Certification

MAINTENANCE AND CERTIFICATION

Smoke in the Cabin—Landing Light Switch Failure

The following occurrence resulted in two aviation safety advisories from the Transportation Safety Board of Canada (TSB).

Background
On September 24, 2007, a Cessna 152 aircraft took off from the Oshawa Municipal Airport, Ont., with the pilot and passenger on board, destined to Kingston, Ont. Just after clearing the control zone, the pilot and passenger noticed an electrical odour and observed a small fire and smoke emanating from the bottom of the left dash panel where the aircraft lighting switches were located. The passenger, sitting in the right front seat, reached for and discharged the fire extinguisher. The fire was quickly extinguished, but the extinguishing agent clouded the cockpit, reducing visibility. The cockpit windows were opened and visibility improved considerably. The aircraft returned to the Oshawa airport and landed without further incident. The pilot suffered a minor burn to his leg when the plastic instrument panel melted and dripped onto his jeans. The TSB issued Final Report A07O0264 on January 14, 2009, regarding this occurrence.

Front of instrument panel
Front of instrument panel

The TSB determined that the landing light switch installed in the occurrence aircraft was beyond its design capability and therefore was unsuitable for the circuit it was controlling. Excessive heat from arcing and oxidization within the switch weakened the switch structure and contact support, allowing the contacts to fall out or be exposed. Arcing from the contacts caused oil residue to flash, which ignited a nearby dust accumulation and started the fire. Combustion was sustained by the plastic instrument panel. The TSB stated that similar landing light switch systems are incorporated on most of the Cessna 100-series aircraft, thereby increasing the likelihood of a similar event. The TSB issued two aviation safety advisories as a result of their investigation.

Advisory No. 1: Landing light switch failure
The landing light electrical circuit is composed of a 15-amp push-to-reset circuit breaker in series with a single pole, single throw rocker switch, which is in series with a 28 VDC 250-watt incandescent lamp. The switch and the circuit breaker are located on the lower instrument panel to the right of and above the pilot’s knee when seated in the left-hand seat. The engine oil pressure and temperature gauges are located directly above the landing light switch. The oil pressure gauge is connected to the oil-carrying pressure line, which is directly connected to the engine. This type of circuit and instrument panel layout are common amongst the 100-series Cessna aircraft.

The switch was identified as a rocker-style switch rated at 10A 250VAC, 15A 125VAC, 3/4HP125-250 VAC. No DC ratings were found for this switch. The switch showed evidence of melt damage beginning at the base and progressing upward on both sides. The same damage was evident on the interior of the switch. The switch exterior had a thick coating of dust and an oily residue, which was also found inside the switch. A scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis of the residue indicated that it might have been engine oil.

The landing light circuit wires remained attached to the contact but showed evidence of fire damage near where the contact enters the switch. The contact was coated with the plastic casing material and when the surface was examined there was evidence of repeated arcing, which had severely eroded the contact’s surface. Arcing within the landing light switch could have provided the ignition source necessary for a fire to start. The dust covering evident on the switch and the oil residue provided by possible seepage from the oil pressure gauge line located above the switch may have provided the kindling necessary to start a fire. The oil would consistently reach its flash point when exposed to arcing, and when it was in proximity to the dust it would cause the dust to ignite. A small section of the plastic instrument panel was tested for flammability by introducing a direct flame to the plastic. The piece of panel readily ignited and sustained flame. It also produced gases that were quite harsh when inhaled, and without sufficient ventilation may cause some incapacitation to the pilot.

Rear of instrument panel
Rear of instrument panel

According to the U.S. Federal Aviation Administration (FAA) Advisory Circular 43.13-1B, chapter 11 (pages 11–17), because of the initial current encountered by switches controlling 28 VDC lamp loads (incandescent lamps), the switches should have a derating factor of 8. This aircraft’s switch controls a 250-watt lamp in a circuit powered by 28 VDC, and should have a minimum DC current rating of 71 amps. The switch from the aircraft had an AC rating. The Advisory Circular has a warning that reads “Do not use AC derated switches in DC circuits. AC switches will not carry the same amperage as a DC switch.” The switch manufacturer was contacted and provided with the landing light circuit and switch information. After evaluating the information, they confirmed that the switch was not designed to handle the lamp loads described.

The circuit breaker was identified as a 15-amp push-toreset circuit breaker (CB), Cessna part number S1360-15L. The purpose of the CB in the circuit is to protect the circuit wiring, not the components attached to the wiring. The 15-amp thermal-type CB was found to be suitable for the circuit. The CB did not trip after the occurrence but, being the thermal-type of CB, it does not react instantaneously to an over-current condition. This feature is necessary because when the light switch is selected “ON”, the initial current can be as high as 15 times its rated load. If the CB were to react instantly to the initial current it would trip every time the switch was selected “ON”.

A search of the FAA’s service difficulty report (SDR) database by the TSB revealed 23 events similar to this occurrence. The common terms were: smell or smoke in cockpit, landing light switch hot, landing light switch arcing, landing light switch melted, and circuit breaker did not trip.

Due to the number of these aircraft presently in use worldwide, including in flight training schools, the possibility that this type of event may recur on aircraft that have the AC-rated landing light switch installed cannot be discounted. If this type of event were to occur to an inexperienced pilot, or to a student-pilot on a solo flight, the pilot’s attention could be diverted from flying the aircraft to focus on extinguishing the fire, with possible dire consequences.

The TSB suggested that Transport Canada (TC), in co-ordination with the FAA and the aircraft manufacturer, may wish to take action to mitigate or eliminate the threat of fire caused by AC-rated switches in the landing light DC circuit of Cessna 152 aircraft.

Advisory No. 2: Smoke-in-cabin emergency procedures
The pilot and passenger followed the emergency procedures for an electrical fire in the cabin, as per the pilot’s operating handbook (POH). The procedures were performed from memory only. Acting on their own instincts, they decided to open the two cabin windows to quickly improve visibility and improve air quality in the confined area of the cockpit. Their quick actions were successful and the pilot was able to re-channel his full attention to safely flying the aircraft back to the airport.

Reported cases of smoke in the cockpit abound in various types of general aviation (GA) aircraft worldwide. A pilot’s ability to fly the aircraft safely is degraded by the presence of smoke and extinguishing agents in the cockpit. Taking action to remove the smoke and fumes from extinguishing agents would increase visibility and improve the air quality within the aircraft.

To ensure that pilots can quickly eliminate smoke and extinguishing agent fumes from the cockpit, further checklist or procedural items may be required. The TSB therefore suggested that TC, in concert with manufacturers and the regulatory authorities of other countries, may wish to review emergency checklist procedures dealing with smoke and fire on GA aircraft and to include an additional step to eliminate smoke or fumes.

Safety action taken
TC contacted the FAA, the authority for the state of design, requesting their position and possible corrective action. The FAA approached Cessna who developed a corrective action plan.

Landing light switch
The FAA took action to mitigate or eliminate the threat of fire caused by AC-rated switches in the landing light DC circuit of Cessna 152 aircraft. Cessna co-operated with the FAA by issuing Mandatory Service Bulletins MEB09-3 and SEB09-6 dated May 11, 2009, to remove and replace all subject switches used in the landing light as well as the taxi light and rotating beacon circuits in the 100-, 200- and 300-series Cessna models with service life greater than four years. This includes the Cessna 152-series aircraft. These bulletins are to be accomplished within the next 400 hours of operation, or 12 calendar months, whichever comes first. A review of the database shows less than 1 percent of the fleet has been affected by this type of failure. Therefore, the FAA’s course of action has been to disseminate the concern by issuing a Special Airworthiness Information Bulletin (SAIB) CE-09-42, which is available at www.faa.gov/aircraft/safety/alerts/SAIB/.

Smoke-in-cabin emergency procedures
The FAA took action by reviewing the emergency checklist procedures dealing with smoke and fire in GA aircraft and including additional steps to eliminate smoke or fumes. The FAA’s course of action has been to disseminate this information by issuing SAIB CE-10-04, which is available at www.faa.gov/aircraft/safety/alerts/SAIB/. It recommends that owners and operators check their POH or aircraft flight manual (AFM) and add a statement: “to remove smoke and fumes from the cockpit, do the following…” If such a statement does not exist in their POH or AFM, owners and operators are encouraged to contact the aircraft manufacturer for checklist instructions for the removal of smoke or fumes from the cockpit (e.g. closing or opening heating, air-conditioning, or air vents).

Considering the FAA’s issuance of the corresponding SAIB and that Cessna has forwarded the applicable service information to all subscribers of such publications, TC has not taken any additional action at this time.

In closing, TC would like to remind the community that defects, malfunctions and failures occurring on aeronautical products should be reported to Transport Canada, Continuing Airworthiness in accordance with Canadian Aviation Regulation (CAR) 521 mandatory SDR requirements. These reports will serve as supporting documentation to present to the authority for the state of design or the manufacturer when corrective action is necessary.



Canada-U.S. Bilateral Aviation Safety Agreement

by Joel Virtanen, Civil Aviation Safety Inspector, Maintenance and Manufacturing, Standards, Civil Aviation, Transport Canada

It has recently come to Transport Canada Civil Aviation’s (TCCA) attention that more awareness is required on the impact of international agreements on the Canadian aviation industry. This article will help address this concern by focusing on the Canada-U.S. Bilateral Aviation Safety Agreement (BASA), its associated maintenance implementation procedures (MIP), and how they apply to aviation professionals in Canada.

On June 12, 2000, Canada and the United States signed the BASA and designated their respective civil aviation authorities as the executive agents for its implementation. The Agreement can be viewed at: www.tc.gc.ca/eng/civilaviation/standards/int-baa-usa-2000-3676.htm.

The BASA provides for, among other things, the reciprocal acceptance of airworthiness approvals and environmental testing and approval of civil aeronautical products, as well as approvals and monitoring of maintenance, alteration and/or modification facilities, maintenance training organizations, and maintenance personnel.

Article III (B) of the BASA required that the U.S. Federal Aviation Administration (FAA) and TCCA— being the executive agents for the Parties—draft written methods by which such reciprocal acceptances would be made. This documented process is referred to as the Implementation Procedures generally, and the detailed procedure for the reciprocal acceptance of maintenance activities and personnel is described in the MIP. The MIP can be viewed at: www.tc.gc.ca/eng/civilaviation/standards/int-ta-usaimp2006-menu-3700.htm.

The objective of the MIP is to outline the terms and conditions under which the FAA and TCCA can accept each other’s inspections and evaluations, including FAA-approved Federal Aviation Regulations (FARs) Part 145 repair stations and Canadian approved maintenance organizations (AMO). The MIP also applies to FAA-certificated airmen and Canadian aircraft maintenance engineers (AME). As a result, the findings of compliance and regulatory oversight by either agency will be accepted by the other agency. This will lead to a reduction in redundant inspections without adversely affecting aviation safety.

At the heart of the MIP is the requirement for a Canadian operator or AMO performing maintenance on U.S.-registered aircraft to first comply with its own maintenance regulatory requirements—including those prescribed by Canadian Aviation Regulations (CARs) Part V, Subparts 71 and 73—and then with the special requirements prescribed by the FAA and described in the MIP. The reverse is true for FAA-approved Part 145 repair stations performing maintenance on Canadianregistered aircraft—they must first comply with U.S. maintenance regulatory requirements, and then with the special requirements prescribed by TCCA.

AMOs and FAA-approved Part 145 repair stations must develop and incorporate a supplement to their own approved maintenance policy manual, or equivalent. The supplement must address all of the other aviation authority’s special requirements, as identified in the MIP. The completed supplement must be submitted to the organization’s own civil airworthiness authority for approval.

Who needs a supplement?
Any Canadian AMO working on U.S.-registered Part 121 or 135 aircraft requires a TCCA-approved FAA supplement to their Maintenance Policy Manual (MPM). The supplement must meet all of the conditions outlined in Chapter 3 of the MIP, which identifies the special conditions set forth by each respective civil aviation authority. Interestingly, it is TCCA that will approve the FAA supplement, and not the FAA.

Any Canadian CAR Part VII operator who has work done on their aircraft in the United States by an FAAapproved Part 145 repair station must ensure that the repair station has an FAA-approved Canadian supplement to their Repair Station Manual (RSM). It is important to note that neither the FAA nor TCCA will issue a supplement approval number in respect of approved maintenance facilities. It is the operator’s responsibility to ensure that the facilities that they intend to use are approved.

What is in a supplement?
The supplement is essentially a bridging document for the differences between the requirements for Canadian AMOs and FAA-approved Part 145 repair stations. Some of the topics covered are: major repair reporting in accordance with the registered authority’s requirements; reporting of service difficulties and suspected unapproved parts to the appropriate authority; requirements and procedures for repairs to be done in accordance with air carriers’ procedures and with data approved by the authority of registry; requirements for major repairs to be signed by an Inspection Authorization in the U.S. and an independent AME in Canada; requirements for procedures to address the registered authority’s airworthiness directives; requirements for procedures to control the maintenance; training program differences; procedures to ensure separation of quality assurance functions from maintenance functions; procedures to ensure that the work does not exceed the ratings or scope of the organization; a requirement to understand the English language (for Canadian AMOs); and a requirement to allow inspections by both authorities.

Who can sign off an annual inspection?
Annual inspections are excluded from the application of the BASA and MIP. A Canadian AME cannot sign off an annual inspection on U.S.-registered aircraft, and FAA-certificated airmen cannot sign off annual inspections on Canadian-registered aircraft. This situation exists due to the differences in our regulations and has been recognized and mutually agreed to by TCCA and the FAA.

How are components affected?
Overhauled and repaired components received from the United States with an Authorized Release Certificate (FAA form 8130-3, Airworthiness Approval Tag) are acceptable for use on Canadian-registered aircraft as long as the repaired parts or components are received from repair stations located within the continental United States, or the Districts of Columbia or Puerto Rico.

Maintenance conducted by FAA-approved foreign repair stations is not acceptable for use on Canadian aircraft since foreign repair stations are not covered by the BASA. Other international agreements should be consulted to determine the eligibility of repaired or overhauled aircraft, parts or components that originate from foreign jurisdictions.

Since operators could be affected by changes, and agreements are reviewed and revised from time to time, it is important to stay informed of the latest changes to the BASA. It is good practice to always check the document’s revision date to see if amendments have been made since the document was last reviewed. Compliance with foreign agreements is necessary and relatively simple as long as you are familiar with the requirements. All international agreements are posted on the TCCA Web site: www.tc.gc.ca/eng/civilaviation/standards/int-menu-3668.htm. For further details and guidance, please refer to Advisory Circular (AC) 571-002—Canada and United States Bilateral Aviation Safety Agreement Maintenance Implementation Procedures at: www.tc.gc.ca/eng/civilaviation/opssvs/managementservices-referencecentre-acs-500-571-002-490.htm.

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