Calculating ETPs for GA Aircraft: Business Aviation Guide

PT 5 M minute read

There’s no regulatory requirement for general aviation (GA) operators to calculate Equal Time Points (ETPs) when planning and filing flight plans. However, ETP planning is a best practice procedure most operators choose to make as part of the pre-flight planning process.

The following is an overview of what you need to know:

ETP Definition

An ETP is a geographical point in the flight where the aircraft would have the same flying time to continue on to a given airport or to turn back to another suitable airfield. While the ETP is generally close to the midpoint of a flight leg this is dependent upon wind factor. If, for example, you’re flying from San Francisco (KSFO) to Honolulu (PHNL), the ETP would be the coast in/coast out point to PHNL or back to KSFO. If you’re flying into headwinds, however, the ETP will be closer to PHNL than to KSFO.

Purpose of ETPs

An ETP is used as a critical point based on an emergency situation. Such emergencies include depressurization, engine failure, and/or in-flight medical emergencies. Note that ETPs often vary, depending upon the particular emergency scenario and flight level you’ll need to descend to. For depressurization at cruise altitude, the norm is to descend to 10,000 ft, engine failure often means descending to 25,000 ft. and in cases of medical emergency flight level changes when required, and will depend on the type of emergency. In practice, actual required changes in flight level will depend on the “operational specs” of the particular flight department.

Flight Plan Considerations

Not all flight plans contain ETPs as this is at the discretion of the individual operator. Most operators calculate ETPs when flying over large bodies of water or significant Arctic, Siberian, or jungle regions. But, in some cases, operators choose to have ETPs when operating over smaller bodies of water and even land masses — such as the Gulf of Mexico or even Anchorage (PANC) to Houston (KHOU). To calculate or not to calculate ETPs always depends on a particular flight department’s ops specs. In general, it’s best practice to have ETPs on flight plans.

Weather Considerations

There are weather recommendations and minima to consider when planning ETPs. Ideally, the location should have at least a 500 ft. ceiling and one statute mile visibility to be considered viable. However, in the case of limited ETP options the operator might consider a 200 ft. minimum ceiling and ½ statute mile visibility. You’ll also want to ensure there are no NOTAMs that could restrict operations to the ETP.

ETPs vs. ETOPs

ETPs differ from Extended Twin Engine Operations (ETOPs) points in that ETPs are not usually filed with flight plans while ETOPs points are. With an ETP you do not need to notify the particular airport or arrange service availability at the location, while you must do this with ETOPs points. Additionally, including ETOPs points in a flight plan may incur local airport changes whereas this is not the case with ETPs.

Filing ETPs

ETPs differ from Extended Twin Engine Operations (ETOPs) points in that ETPs are not usually filed with flight plans while ETOPs points are. With an ETP you do not need to notify the particular airport or arrange service availability at the location, while you must do this with ETOPs points. Additionally, including ETOPs points in a flight plan may incur local airport changes whereas this is not the case with ETPs.

ETP Requirements

ETP requirements will vary from one operator to another depending on the ops specs, crew preferences, weather conditions, and region of flight. ETPs are always recommended over regions such as large bodies of water and flying over landmasses with few airport options. Note that unlike ETOPs, when filing a flight plan, ETPs won’t incur certain airport charges, so it’s a benefit for the flight to have additional options to consider.

When a variety of equal time point (ETP) possibilities are available, operators have the option of being more selective and choosing airports with the best available service and support capabilities. However, there are times when available ETPs may be few and far between — such as over the Siberian region — and you may need to work with options that are less than ideal.

Selecting ETPs

Ideally, selected ETPs should be airports of entry (AOEs) that are open at the time you’ll be in the vicinity, and have an instrument landing system (ILS), runway lights, fuel availability and all required services. It’s recommended that the operator and 3rd-party provider have a conversation on specific ETP requirements, such as runway length, runway surface material, availability of services and options for scheduled commercial flights out of the location. But, there are some cases — including depressurization or engine fire — when you just need to get on the ground quickly. In such cases, operators will be less selective in terms of ETP airport amenities and may consider landing in higher-risk areas. In cases of emergencies, you may need that first available viable airport, even if it’s not an AOE.

Top issues with ETPs

When flying over large sparsely populated areas there may be limited options in terms of ETPs and you may need to consider the possibility of a “wet footprint.” For example, on a polar routing from Teterboro (KTEB) to Beijing (ZBAA), the nearest airport may be several hundred miles away from a certain point on your flight plan and could be restricted to a Russian military base. On a flight across the South Atlantic your only practical ETP may be Ascension Island (FHAW), a joint U.S./UK military base that does not technically allow its airfield to be used as an alternate or an ETP. Another issue that may come up is choosing an ETP with runway issues — Kanton Island (PCIS) has a 7000 ft. runway but it’s a rough coral surface, has a lack of essential services and/or closures/curfews in effect.

Wet Footprints

A wet footprint is an area encompassing the distance on either side of an ETP where if the aircraft is required to descend it will not have sufficient fuel to make either the destination or the point of departure. The size of the wet footprint area is determined by total fuel onboard, the altitude that the aircraft will descend to and the wind factor. In the event of an emergency descent to 10,000 ft. as a result of depressurization, fuel burn will be much higher than normal and the wet footprint may be extended. Part 135 charter (non-scheduled commercial) flights are prohibited from having wet footprints. While Part 91 private non-revenue operators do not have this restriction it’s always best practice to avoid wet footprints. Some operators will absolutely avoid any chance of a wet footprint scheduling an additional stop in the flight plan where possible, while other operators will look at options in minimizing potential wet footprints. For example, you may be able to eliminate a particular wet footprint by descending only to 15,000 or 20,000 ft. in event of depressurization. Doing so, however, may require carrying additional oxygen onboard.

Additional Considerations

Selection of ETPs should reflect the particular requirements of the operator as well as the nature of the flight. For example, for air ambulance operations an ETP location close to a capable medical facility will be a plus. Another consideration may be selecting ETPs with adequate scheduled commercial services, so that the principal and/or passengers may proceed on to meetings at their intended destination.

Work with your 3rd-party provider

NBAA, FAA and other sites provide useful information on ETP selection. But, having your 3rd-party provider involved in the flight planning and ETP process will not only save you two to three hours in planning time but improve ETP coordination. Your 3rd-party provider will evaluate ETPs against the latest weather conditions/predictions, confirm service availability and present options to eliminate any potential wet footprints.

When planning flight plans and ETPs it’s important that your 3rd-party provider has your current flight department operational specifications on file. This will help ensure that the best and safest options can be determined for your flight.

Successfully Planning ETPs

Planning ETPs for longer flights over water or sparsely populated land masses is always recommended. Given sufficient lead time, and working with an experienced 3rd-party provider, ETP options are always available. However, these choices must take into account the operational specifications of the particular flight department and any other requirements needed for the particular leg.

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