Oxygen Escape Routes

Oxygen Escape Routes are used to calculate a safe route through obstacles in excess MORA of FL100 in the event of cabin depressurization during a flight. In the event of cabin depressurization, operators must descend to FL100 where outside temperature, pressure and oxygen density are sufficient to allow survival of passengers and crew. The descent in the case of an Oxygen Escape Route is time-dependent, i.e., it must take place before the oxygen supply of the aircraft is depleted. This time is referred to as the oxygen endurance time. The aircraft can stay at the highest possible flight level to avoid obstacles until it must descend in order to get to FL100 within the oxygen endurance time. Oxygen Escape Routes begin at the first post-TOC waypoint with a MORA of greater than FL100 and ends at the first post-TOD waypoint with a MORA of more than FL100 See below for an illustration of the applicable portion of a sample route for which Oxygen Escape Routes are generated.

When calculating Oxygen Escape Routes, the aircraft must be able to safely descend to FL 100; landing does not need to occur during this time.

Escape routes are provided for route legs with MORA values lower than 10 000 ft, unless no obstacles with a MORA value greater than 10 000 ft impact the flight for a distance of 500 NM.

The determination of an Oxygen Escape Route also must take into account airport suitability, i.e., which airports are able or not able to accommodate the aircraft in the event of a depressurization emergency.

NAVBLUE Flight Plan automatically generates Oxygen Escape Routes if the Oxygen Endurance time is set in FOMS Menu 220 (Aircraft Characteristics Program). Some format changes are required to implement this. Contact NAVBLUE for assistance.

N-FP’s default search graph for escape routes restricts the flight to remain within named airways and must always connect to a STAR at the diversion airport. You may see longer diversion routes due to lack of available connections to closer airports.

In Airline Code Parameters, you can enable DCT Escape Routes, opening up the search graph further to use DCT segments, and allowing the search graph to connect directly with Initial Approach Fixes, bypassing STARs.

Furthermore, if you define an Escape Route Station in the plan screen, when the above setting is enabled, N-FP attempts to plan escape routes to the defined airports, even if no approach is available.

Oxygen Endurance Penalty

Since the Oxygen Escape Routes always start at a waypoint along the route, and it is unlikely that depressurization will occur precisely at a waypoint, NAVBLUE Flight Plan 10-1 considers how to handle a depressurization event between waypoints. To do this, it applies an oxygen endurance penalty to the oxygen endurance time. The size of the penalty is determined by comparing the traversal time of the leg before and after the diversion waypoint. The larger of the two times is taken, cut in half, and applied to the oxygen endurance time as a penalty, effectively reducing the oxygen endurance time. This worst-case scenario approach to determining how long (and by extension how far) the aircraft can travel before completing its descent introduces a degree of conservatism to the calculation. Ultimately, the pilot must use discretion as to whether to continue to the next waypoint or to return to the previous one.

Each entry is independent and the times displayed are not cumulative. View ExampleView Example