In aviation, there’s a critical concept known as Equal Time Point (ETP), often utilized in Extended Range Twin Engine Operations (ETOPS). ETP is the point along a flight route where it takes the same amount of time to reach both the destination and the departure point in case of a return. To illustrate, let’s consider two aerodromes, A and B, 400 nautical miles apart. If you depart from A with a True Air Speed (TAS) of 400 knots, it will take an hour to reach B, making the ETP 30 minutes after departure, allowing 30 minutes for a return to A.
However, real-world scenarios are more intricate due to the influence of ground speed affected by prevailing winds. For instance, with a tailwind on your direct route from A to B, the ETP moves closer to A, as turning back would mean encountering a headwind, which slows down the aircraft.
ETP plays a pivotal role in ETOPS, which grants airlines the ability to extend the time they can operate with just one engine. In non-ETOPS situations, an aircraft can fly for a maximum of 60 minutes with one engine out. ETOPS certification extends this duration, often up to 180 minutes. To meet ETOPS requirements, the aircraft must be within a certain flight time of a suitable aerodrome in case of an engine failure. Calculating this involves determining how far the aircraft can travel at the approved ETOPS speed. For example, if the approved speed is 320 knots, the aircraft can cover 960 nautical miles in 180 minutes. Drawing circles with radii of 960 nautical miles around alternate aerodromes on a chart reveals the ETP.
In ETOPS, the ETP can be a crucial factor in fuel planning, depending on the nature of the failure. While an engine failure itself may not necessarily lead to a fuel crisis, other failures like cabin pressurization issues might necessitate a descent to lower altitudes, burning more fuel. Therefore, fuel is loaded considering these potential critical scenarios.
Beyond fuel considerations, crossing the ETP is significant because you’ll only have enough fuel to divert to one of the possible alternate aerodromes. Consequently, before reaching the ETP, thorough checks must ensure that the weather conditions at the chosen alternate aerodrome are suitable for a safe landing. Such diversions are rare due to stringent dispatch weather requirements for ETOPS flights, minimizing the likelihood of weather deteriorating after departure.
Author – Nischal Paudel
Pilot
