Equivalent Safety Finding UK.ESF.F.0002 (Terrain Information Display and Synthetic Vision System) Consultation: CS-25 Large Aeroplanes

For comments on the proposal that the CAA introduces a special condition to be used for the crashworthiness conditions of a conformal rear centre fuel tank installation on a large transport aeroplane.

The UK CAA is consulting on an Equivalent Safety Finding that is applicable to CS-25 Large Aeroplanes.

This Equivalent Safety Finding provides the compensating factors to reach an equivalent level of safety as an alternative to compliance with CS ACNS.E.TAWS.030 (b)(3), (b)(4), and (e) based on the availability of additional terrain information displayed on other windows of the PFD.

The Consultation Paper Equivalent Safety Finding UK.ESF.F.0002 Issue 1 provides the full detail of the identified issue, and the associated Equivalent Safety Finding.
You Said

We received 3 responses.
The first response concerned the need to ensure specific training in a realistic environment associated with the propose alternative approach. The response also comments that the TID is provided whenever required in both normal and reversionary modes.

The second response described two different scenarios that are perceived by the commenter as effective in implementing SVS and terrain information display. The first scenario refers to a SVS implementation that changes the colour of the terrain when it becomes a threat to the aircraft. The second scenario refers to a top 3D SVS view being supplemented by a bottom HSI view where terrain is represented in green, yellow, red.

The third response raised several comments around the implementation of the proposed mitigating factors. Dependent on the solution implemented, comments were raised including the potential for fore-shortening effects if the terrain information display compresses the SVS, the need for the pilot to integrate the information given on the two displays (SVS and TID), and the ability of the pilot to identify FPV when overlapping terrain.

We acknowledge the responses and thank the responders for their suggestions.
For the first response, the comment is not incorporated. The CAA consider that the training element is out of contest in the ESF, and that the subject of the reversionary mode of the "alerting display" is covered by the current compensating factor in Appendix A section 3.a and the required compliance with the other requirements of the CS ACNS Subpart E that remain applicable.
For the second response, the comment is not incorporated.

The scenarios described are both noted. In particular, the second scenario is considered to be covered within the compensating factors presented which require separate window providing a 2d view of the terrain compliant with CS ACNS.E.TAWS.030 (b)(3) and (b)(4).

For the third response, the comment is not incorporated. The CAA acknowledge the observations presented, however consider that the points raised apply at the design