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 Flight Level (FL) 100 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 greater than FL100 and end at the first TOD waypoint with a MORA of more than FL100. Refer to the illustration below for 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, such as 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. You can contact our NAVBLUE Support on the Support Portal to receive assistance.
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.