Emergency descents must evidently be performed without any collision, therefore obstacle clearance is a central aspect in engine failure regulations. Lateral and vertical clearance rules are both described in CAT.POL.A.215 and CAT.POL.A.220 (Appendix A.1.3 and A.1.4), for OEI and multiple engine failure scenarios, respectively. They should be applied to the net flight path.
The obstacle clearance guidelinesfor OEIwill be the focus of the present Section 6.3, but the reader is encouraged to consult the regulatory transcripts for multiple engine failure in Appendix A.1.4.
6.3.1 Lateral Clearance
On the matter of lateral obstacle clearance margins during OEI situtations, the regulation states:
CAT.POL.A.215 (Appendix A.1.3)
” (c) [...] The net flight path shall clear [...] all terrain and obstructions along the route within 9,3 km (5 NM) on either side of the intended track [...]
(d) The operator shall increase the width margins of [...] (c) to 18,5 km (10 NM) if the navigational accuracy does not meet at least required navigation performance 5 (RNP5). ”
RNP5 means that a navigation system must be able to calculate its position to within a circle with a radius of 5 Nautical Miles (NM) [32].
Figure 6.3: Lateral Obstacle Clearance (Adapted from [21])
6.3.2 Vertical Clearance
Vertical clearance is a safety margin between the net flight path and the obstacles to clear. According to CAT.POL.A.215 (Appendix A.1.3), the en route net flight path has to be determined from the Aircraft Flight Manual (AFM), published by the manufacturer, and must take into account the meteorological conditions (wind and temperature) prevailing in the area of operations. Also, if icing conditions are probable at the diversion level, the effect of the anti-ice system must be considered on the net flight path.
There are two conditions given by legislation, one of which must always be satisfied when performing route studies. If Condition 1 cannot be met, or it shows to be too penalizing in terms of weight, then the route study has to be based on Condition 2 [21].
Condition 1 - 1000ft Clearance CAT.POL.A.215 (Appendix A.1.3)
”[...](b) The gradient of the net flight path shall be positive at least 1 000 ft above all terrain and obstructions along the route within 9,3 km (5 NM) on either side of the intended track. [...]”
The route study methodology in case of an Engine Failure at Cruise Level is as follows [21]:
• From a topographic map, determine the highest obstacle in the regulatory corridor and add 1,000 feet to obtain a height H1.
• From the AFM, determine the net drift down ceiling (H2) at a conservative weight. Choose, for instance, the heaviest possible aircraft weight at the entrance of the constraining area.
• Conclusion:
– If H2 is higher than H1, the route study is completed and the obstacle clearance is ensured at any moment.
Figure 6.4: Vertical Obstacle Clearance - 1000ft Rule (Adapted from [21])
– If H2 is lower than H1, then a more detailed study based on Condition 2 shall be conducted, or a weight limitation at takeoff established, or a new route found.
Condition 2 - 2000ft Clearance
Condition 2 is only related engine to failures that occur during the cruise phase, which corresponds to the focus of this work’s objective. When Condition 1 is not met, or when it is too limiting in terms of weight, a drift down procedure should be planned, as detailed below:
CAT.POL.A.215 (Appendix A.1.3)
”[...](c) The net flight path shall permit the aeroplane to continue flight from the cruising altitude to an aerodrome where a landing can be made in accordance with CAT.POL.A.225 or CAT.POL.A.230, as appropriate. The net flight path shall clear vertically, by at least 2 000 ft, all terrain and obstructions along the route within 9,3 km (5 NM) on either side of the in- tended track [...]”
It must be possible to perform an emergency descent and clear any obstacle by at least 2000ft, at any given point along the operational route. When a drift down procedure has to be initiated, three different scenarios exist:
• Turn Back - Turn around and follow the current route in the opposing direction
• Divert - Abandon the current route and proceed along an alternative one
• Continue - Continues along the current route
The methodology which allows to decide which of the three scenarios each point of a route corre- sponds to can be found in Airbus’ ”Getting to Grips with Aircraft Performance” [21]. In the context of the
Figure 6.5: Vertical Obstacle Clearance - 2000ft Rule (Adapted from[21])
the descent can be performed along the planned route. In other words, it tests scenario three (”Con- tinue”) and informs the user if this scenario is possible given current aircraft status and atmospheric conditions.
7. Emergency Profile Application (EPA)
This chapter describes how the Emergency Profile Application (EPA) was developed, what objectives it was set to achieve, the tools used for its development, as well as its internal structure and organization.
The chapter starts off with a description of the application in Section 7.1. Section 7.2 presents the objectives that the application should achieve. Section 7.3 lists the software and tools used for building the application. The symbology used in flowcharts throughout Chapter 7 is explained in Section 7.4.
Section 7.5 presents the application’s structure, dividing it into four main steps. These four steps are presented in Sections 7.6 through 7.9. The final Section 7.10 presents some important information regarding the usage of the EFB database by EPA.
7.1 Description
EPA is an application that allows the computation and verification of emergency flight profiles for de- pressurization and engine failure scenarios. It computes flight performance using Airbus’ software, and verifies if the flight profile can be executed, given current aircraft location and navigational constraints.
EPA’s tools are targeted at Flight Crew members (Captains and First Officers) and Flight Operations Officers. By using updated meteorological conditions, the most reliable information is used, thus verifying if the original procedures and escape routes released by flight dispatchers are still valid.
At this point, a connection between the EFB and the aircraft is inexistent. This means that aircraft data like altitude, weight and coordinates have to be estimated, manually set or hardcoded. In the future, parameters like these could be automatically sent from the aircraft to the EFB through a direct data link.
This would unlock the full potential of EPA. The software can then be expanded to analyze alternative routes in case of failure, as updated meteorological information gets released. This would allow the software to scan a whole route, identify critical points automatically and suggest appropriate escape routes. The present version is the computational foundation upon which TAP’s EFB team can build these additional features.