HC Deb 04 April 1960 vol 621 cc6-8W
Mr. Scott-Hopkins

asked the Minister of Aviation what study has been made by Her Majesty's Government, within the International Civil Aviation Organisation, of the report by the United States Federal Aviation Agency, entitled Operational Test of Mark 10 Decca System in C-131 Fixed-Wing Airplane.

Wing Commander Bullus

asked the Minister of Aviation his intentions regarding the use of the Decca Navigational Aid system in British aircraft, following the trials that have been made in the United States of America, the results of which have been reported to the International Civil Aviation Organisation.

1960. Mr. Sandys

This report has been circulated to members of the International Civil Aviation Organisation. I do not consider that the conclusions it seeks to draw can be accepted as valid. The following letter, expressing the United Kingdom's views, has been sent to the Secretary General of the Organisation.

The United Kingdom Representative on the Council of the International Civil Aviation Organization.

912, International Aviation Building,

Montreal, Canada.

th March,

Sir,

United States F.A.A. Reports on Decca System

I have the honour to acknowledge receipt of the report entitled "Helicopter Operations Program, Phase 1" and the supplementary report "Operational Test of Mark 10 Decca System in C-131 Fixed-Wing Airplane" issued by the United States Government and conveyed under cover of your letter A10/15 SR70/2–60/19, dated 16th February, 1960.

2. The documents have been studied with considerable interest and the United Kingdom is pleased to note, in the case of the report "Helicopter Operations Program, Phase 1", evidence of an objective evaluation of the Decca system in an application which it has long advocated. The useful data collected during this first phase of the programme is largely in accord with the results of earlier work carried out in the United Kingdom. It is hoped, however, that the evaluation team will find At possible to supplement the relatively small amount of data on system accuracy in the interests of statistical analysis.

3. The United Kingdom is greatly encouraged by the declared intention of the United States, on the basis of the results obtained during Phase 1, to proceed with Phase II, under IFR conditions, of the Helicopter Operations Programme. In anticipation of receiving a further report on this second phase of the programme, the United Kingdom prefers to reserve more detailed comment.

4. It is with regret that the United Kingdom feels bound to observe that the supplementary report "Operational Test of Mark 10 Decca System in C-131 Fixed-Wing Airplane" suffers by comparison with the principal document and cannot be accepted in the same category of objective reporting. Experience of system evaluation extending over many years strengthens the belief that the approach to the subject has in this case been hasty and ill-conceived. The United Kingdom is accordingly unwilling to allow the issue of the Supplemental Report at the present time and in the present circumstances to pass without comment, and makes the following observations in the true spirit of international cooperation.

5. The expressed purpose of the trials dealt with in this report was "not to conduct a precise programme but rather to assess, through pilot experience and opinion, the extent to which the automated Mark 10 components might facilitate air navigation in typical United States air traffic control environments ". If meaningful results are to be obtained from a subjective trial of this kind, it is essential to take great care to ensure that neither the trial conditions nor the method of assessment used can introduce large biasing factors. Unfortunately, no attempt seems to have been made in these trials to guard against the presence of such factors or to make allowance for them.

6. Serious biasing factors present in these trials were:

  1. (i) A large proportion (approximately half) of the route mileage flown was in areas of coverage and accuracy where the Decca Mark 10 system is not, and has not been claimed to be, entirely satisfactory for navigation of all ATC procedures.
    • Note 1: The areas of Decca coverage suitable for various ATC uses are defined by the United Kingdom in paragraphs 49 and 50 of Appendix A of COM/OPS/ RAC Working Paper COR-WP/18.
  2. (ii) The type of questionnaire used does not permit statistical examination because there is no discrimination between operationally significant and insignificant faults.
    3. 8
  3. (iii) The tests were conducted on low power chains in conditions of relatively high background noise level. The radiated power was less than normally provided from other operational chains and appears to have been inadequate for the purpose of the trials.
  4. (iv) The design of the flight log charts was in some instances unsuitable for the declared purpose of the trials.
    • Note 2: United Kingdom requirements for design of flight log charts are published in Attachment A to Appendix A of the Report of the Special COM/OPS/ RAC Meeting (Doc. 7973 COR 1/1).

7. There is no evidence in the report that these serious biasing factors have been given due weight, either in the design of the pilots' questionnaire or in the analysis of results. In these circumstances, it is clearly unwise to draw firm conclusions. The fact that, despite these shortcomings, an attempt to draw conclusions has been made, casts serious doubts on the value of the report from any aspect.

8. I should be grateful if these comments could be brought to the notice of those member States to which copies of the United States reports have been circulated.

I am, Sir,

Your obedient servant.

(Sgd.) J. H. RIDDOCH.

The Secretary General,

International Civil Aviation Organisation, Montreal.