Air transportation safety recommendation A91-21

Reassessment of the response to Recommendation A91-21

Manufacturer's recommendations - Letters-to-operators - Compliance requirements

 Recommendation A91-21 in PDF [157 KB]

Background

On 15 September 1988, a Hawker-Siddeley HS-748, was in cruise flight at 3,000 feet in visual flight conditions while on an instrument flight rules flight to Ottawa International Airport from Montreal/Dorval Airport. Coincident with a remark by the captain pointing out a ground feature, the aircraft commenced a full aileron deflection roll to the left. The aircraft rolled through 465 degrees and descended to impact, with a final speed of approximately 290 knots. In the last stages of the accident manoeuvre, a maximum vertical acceleration of approximately 4.7g was recorded. Both crew members on board were killed, and the aircraft was destroyed.

The investigation determined that the aileron control system was asymmetrically rigged, making it susceptible to aerodynamic overbalance. The operator had not conducted the required post-maintenance flight tests of the aileron control response.

Contributing to the accident were the design of the aileron system; ambiguous and incomplete maintenance instructions; a lack of published information for flight crew concerning aileron system performance and possible emergencies; and the presence of factors which may have led to the development of flight crew fatigue.

As a result of the investigation of this occurrence, the TSB forwarded six recommendations to TC; four dealt with aircraft aileron overbalance, and two centered on manufacturer notices‑to‑operators (NTO).

The Board concluded its investigation and released Aviation Investigation Report A88H0011 on 18 June 1991

TSB Recommendation A91-21 (June 1991)

The country of manufacture of an aircraft is obligated by section 4.2 of annex 8 of the International Civil Aviation Organization (ICAO) Standards to transmit to contracting states any generally applicable information which it has found necessary for the continuing airworthiness of an aircraft and for the safe operation of an aircraft. To further ensure the continuing airworthiness of Canadian-registered aircraft, TC routinely reviews all manufacturers' service bulletins and, if required, issues Airworthiness Directives (ADs). TC's review of service bulletins is in accordance with paragraph 5 (b) of section 571.101/4 of the Airworthiness Manual Advisory (AMA), which states that manufacturer's recommendations, such as service bulletins (which primarily concern aircraft maintenance) and Letters-to-Operators (which primarily concern aircraft operation) are assessed by TC to determine their acceptability.

Although all service bulletins are reviewed by TC, Letters-to-Operators, including NTOs, are usually reviewed by TC only if a specific request to do so is received from an operator. This practice could result in TC overlooking vital operational or maintenance related information which might otherwise have resulted in an AD being issued.

In addition, operator compliance requirements with respect to service bulletins are detailed in Notice to Aircraft Maintenance Engineers and Aircraft Owners (NAME-AO) No. 26/83; however, compliance requirements with respect to Letters-to-Operators have not been promulgated.

Therefore, the Board recommended that

the Department of Transport clarify the operator compliance requirements with respect to Letters-to-Operators.
TSB Recommendation A91-21

Transport Canada's response to Recommendation A91-21 (February 1992)

It is Transport Canada's policy to review manufacturers' Service Bulletins and Airworthiness Directives issued by foreign airworthiness authorities, applicable to aircraft types registered in Canada. Although other service and maintenance documents that come to Transport Canada's attention may-be assessed, present policy does not, because of the amount and diversity of the information involved, include the review of all service and maintenance related correspondence between manufacturers and operators.

Transport Canada agrees to review the present policy and will undertake an evaluation of the matter of review of Letters-to-Operators in terms of potential safety benefits, cost impact, administrative feasibility and related factors.

TSB assessment of Transport Canada's response to Recommendation A91-21 (March 1992)

In issuing recommendations A91-20 and A91-21, the TSB emphasized that the omission of the operational content of the manufacturer's “Letters-to-Operators” was of prime concern; however, TC's response seems to focus on airworthiness concerns and completely skirts the operational issue. Nevertheless, TC's proposed review of their present policy and evaluation of the review process of Letters-to-Operators, plus a stated intent to produce a new Airworthiness Manual Advisory (AMA) may encompass the operational considerations as well as the airworthiness ones.

The intended review by TC, if broad in scope, could address the intent of Recommendations A91-20 and A91-21. It will be the results of the TC review, and subsequent action that should indicate if the deficiencies of Recommendations A91-20 and A-91-21 have been fully addressed.

Therefore, the response to the recommendation is considered to be Satisfactory in Part.

Board reassessment of Recommendation A91-21 (November 1996)

In August 1995, Transport Canada completed its final report entitled “Letters-to-Operators Survey”.

Therefore, the assessment remains as Satisfactory in Part.

Transport Canada's response to Recommendation A91-21 (April 1997)

TC will produce a new airworthiness manual advisory that will clarify the compliance requirement for known categories of manufacturer's instructions for continued airworthiness. This advisory will take into account any pertinent result from the study proposed in A91-20.

Board reassessment of Recommendation A91-21 (November 1997)

Transport Canada will produce a new Airworthiness Manual Advisory (AMA) designed to clarify the compliance requirement for each category of manufacturer's instructions.

The initial draft was completed as of 02 April 1997. Further work is on hold due to higher priorities.

Therefore, the assessment remains as Satisfactory in Part.

Board reassessment of Recommendation A91-21 (January1998)

No changes since the last reassessment.

Therefore, the assessment remains as Satisfactory in Part.

Board reassessment of Recommendation A91-21 (January 2004)

A review of recent TC Airworthiness Manual Advisories (AMAs) could not confirm TC issued an AMA regarding the handling of manufacturers' instructions. However, despite the fact that no specific advisory material was issued with regards to LTO review, the residual risk from the safety deficiency is considered “low”.

As such, Further Action is Unwarranted with respect to A91-21 and the status is set to Inactive.

Board review of Recommendation A91-21 deficiency file status (April 2014)

The Board requested that A91-21 be reviewed to determine if the Deficiency File Status was appropriate. After an initial evaluation, it was determined that the safety deficiency addressed by Recommendations A91-21 needed to be reassessed.

A request for further information was sent to Transport Canada and a reassessment will be conducted upon receipt of Transport Canada's response.

Therefore, the assessment remains as Satisfactory in Part.

Consequently, the status of Recommendation A91-21 is changed to Active.

Transport Canada's response to Recommendation A91-21 (June 2018)

Transport Canada (TC) agrees in principle with the recommendation.

TC agrees that Part VII of the Canadian Aviation Regulations (CARs) may require amendments in order to clarify operator responsibilities regarding letters-to-operators. TC will prepare an issue paper for the Regulatory Steering Committee identifying the issue and recommending the development of a Notice of Proposed Amendment (NPA) to introduce an evaluation program for Part VII Operators. 

TC expects to have the issue paper developed in June 2018, in order to present to the Steering Committee.

Board reassessment of Transport Canada's response to Recommendation A91-21 (February 2019)

To date, the following actions have been proposed by Transport Canada (TC) to address the safety deficiency identified in Recommendation A91-21, regarding the clarification of the operator compliance requirements with respect to Letters-to-Operators:

  • In 1992, TC intended to review its policy and undertake an evaluation of the review of Letters-to-Operators in terms of potential safety benefits, cost impact, administrative feasibility and other related factors;
  • In 1995, TC completed a report entitled “Letters-to-Operators Survey”; and
  • In 1997, TC completed the initial draft of an airworthiness manual advisory to clarify the compliance requirements for each category of manufacturer's instructions.

Apart from the Letters-to-Operators Survey Report, none of the other actions previously proposed by TC was completed. In its latest response, TC indicates that it will prepare an issue paper for the Regulatory Steering Committee identifying the issue and recommending the development of a Notice of Proposed Amendment to introduce an evaluation program for Part VII operators. The issue paper was presented to the Regulatory Steering Committee on 27 June 2018, and was accepted. TC now plans to develop the draft Notice of Proposed Amendment by early March 2019.

This recommendation was issued more than 27 years ago. The Board is concerned with the protracted delays in addressing the safety deficiency identified in Recommendation A91-21.

The Board notes the progress made in 2018 and hopes that the momentum can be maintained in 2019 so that this safety deficiency can finally be fully addressed. Although the future evaluation program for Part VII operators may address the safety deficiency identified in Recommendation A91-21, until it is fully implemented, the risks to transportation safety remain.

Therefore, the response to Recommendation A91-21 is assessed as Satisfactory Intent.

Next TSB action

The TSB will continue to monitor the progress of TC's proposed evaluation program for Part VII operators, and will assess the deficiency on an annual basis or when otherwise warranted.

This deficiency file is Active.

Date modified: