Equal Time Points (ETPs) in Aviation: A Closer Look at Calculations and Planning

Go On, Or Go Home?

Accurate Equal Time Points (ETPs) calculation is a critical safety function that streamlines decision making in the event of an in-flight emergency. From medical emergencies to depressurization, engine failure, and other critical events, there are instances when pilots need to proceed to the nearest suitable airport as fast as possible, and knowing the ETP supports better decision-making in these time-sensitive situations. 

What Does Equal Time Point (ETP) Mean?

An Equal Time Point (ETP) is a geographical location along a flight route where the time it would take to reach a certain airport is the same as the time it would take to reach an alternative airport. 

A simple example is an ETP between your departure and destination airports.  When you pass this ETP you know it’s quicker to continue to your destination than it is to turn around and return to your point of departure.

A more complex use of ETPs may be used to define the point between 2 enroute diversion airports, for example when crossing an ocean where suitable airports may be hundreds of miles apart.  When one ETP is passed, the next one can be calculated using another airport pair, so you’ll always know the best diversion option wherever you are along your route.

ETP Calculation Formula

The formula to calculate an ETP is as follows:

Ground Distance to ETP = (D)(GS_r)GSc + GSr = NM

To make this calculation, you need to know:

D: the total trip distance

GS_c : Groundspeed to continue to a specific airport at normal cruise altitude

GS_r : Groundspeed to another airport at normal cruise altitude

Let’s look at an example. 

Say D = 2500 NM, GS_c = 400 knots, and GS_r  = 450 knots.

Ground Distance to ETP = (2500)(450)400 + 450 = 1323 NM

In this example, the midpoint of the journey in zero wind is 1250 NM, so the wind has moved the ETP 73 NM upwind. 

ETOPS Vs. ETPs: The Difference Explained

Regulations do not allow twin-engine aircraft to fly routes that take them more than a certain distance away from a suitable airport unless given specific approval.  This distance, which may depend on the size of the aircraft, typically corresponds to a 60-minute cruise with one engine inoperative (OEI).  Historically, these aircraft were restricted from long-range flights over water due to concerns about the lack of suitable diversionary airports along such routes, and the safety issues that arise from the lack of a third or fourth engine. 

Extended-range Twin Engine Operations Performance Standards (ETOPS) refers to the certification that an aircraft manufacturer receives for a specific aircraft model, allowing twin-engine aircraft to fly routes that bring them more than 60 minutes from the nearest suitable airport. Additionally, aircraft operators must also receive an ETOPS operational certificate and crew members must be approved to operate ETOPS routes. Historically, these aircraft were restricted from long-range flights over water due to concerns about the lack of suitable diversionary airports along such routes, and the safety issues that arise from the lack of a third engine and other redundant systems. 

Twin-engine aircraft receive ETOPS ratings as part of this certification, which dictate how far from a diversionary airport they can go. An ETOPS approval drastically reduces flight distance, time, and costs.

ETOPS entry and exit points are geographical locations defining the ETOPS segment of the flight.  Between these points and, in the event of an engine failure or other emergency, the aircraft would be more than 60 minutes OEI  diversion time to an alternate airport. 

ETOPS and ETPs are both important concepts in aviation; however, there are some key differences between them, including the fact that ETOPS only applies to twin-engine aircraft operating under Part 121 and 135, whereas ETPs apply to all aircraft. 

The ETP and Flight Plan Considerations

While having an ETP on a flight plan is best practice, it is not a regulatory requirement, and their inclusion is usually up to the individual operator and their standard operating procedure (SOP). An accurate ETP is particularly important for longer flights over open water or unpopulated terrain, where the availability of diversionary airfields is limited. During a flight, the ETP may change due to current conditions, and as such, it’s a dynamic parameter that may need to be recalculated as flight plans are updated, or included as a series of ETPs.

In an emergency, including an ETP in the flight plan helps enhance situational awareness and equips pilots with the best possible information when making decisions. ETPs can also impact route planning, fuel planning, and diversion planning, dictating the maximum distance an aircraft can fly from its planned route before a diversion becomes necessary.

‍How to Automatically Calculate and Plot ETPs Using ForeFlight

With ForeFlight, calculating and plotting dynamic ETPs accurately and efficiently is easier than ever.

To determine ETP, the first step is to specify your diversionary airport pairs. For example, to determine ETP between the departure and destination airport, the planner must enter the appropriate departure and destination airport identifiers under ETP Airport Pairs fields.

Dispatch can calculate ETP for more than one airport pair. This ability is useful for when there are numerous suitable diversionary airports along your route of flight. 

Once you’ve added your route in Dispatch, and specified diversion airports, ForeFlight Dispatch will add equal time points on the built-in map and in the Navlog. Dispatch depicts each equal time point on the map as a small gray dot. Additionally, you can enable ETOPS to overlay range rings for each airport and automatically validate the route for each diversion scenario.

To determine which emergency scenario is being depicted by the ETP dot, hover the cursor over the dot for two or more seconds. The pop-up depicts the emergency scenario (e.g. OEI), the airport pair, and the ETE between ETP and the diversionary airports.

Watch a demonstration of this process in the video below:

4 Key Aspects to Consider When Planning an International Flight

If you’re planning a long-range, overwater international flight, be sure to incorporate the following into your flight plan:

ETPs

It’s recommended that you calculate and add ETPs when flying long-range over water or sparsely populated terrain to help ensure effective contingency planning and decision-making in the event of an in-flight emergency. ETP planning helps ensure you have enough fuel and resources available to divert to a suitable airport if needed, even when there are limited possible diversions available.

‍Alternate Airports

In the case of unexpected events, such as restrictive weather conditions, technical difficulties, or airspace restrictions, it’s important to incorporate at least one alternate airport into your flight plan. Not only is this a regulatory requirement, but it also allows you the flexibility needed to navigate variable conditions and unforeseen circumstances effectively. 

Detailed Weather Forecasts

Ensuring that you have access to detailed weather information is critical for a safe flight. The latest weather forecasts for your route and destination should be carefully considered when preparing your flight plan. 

Plan Your International Flight With ForeFlight

ForeFlight’s integrated trip planning capabilities make planning international flights easier and more efficient than ever before. ForeFlight Dispatch delivers a centralized Flight Status View, synchronizing flight data from scheduling applications, trip support, and ForeFlight Mobile and Web applications to radically increase efficiency for flight departments of any size.

Additionally, planners can leverage integrated trip support capabilities with ForeFlight Trip Support, which integrates with your Dispatch account to produce flight plans and share trip documentation seamlessly. ForeFlight’s Trip Support combines global aviation expertise with market-leading technology resulting in reduced risk and exceptional experiences for those counting on you.Finally, integrated Flight Releases synchronize all flight details and documentation, giving relevant crew members immediate access in ForeFlight Mobile. 

The result? 

Seamless, effortless international flight planning, in the palm of your hand.

Try ForeFlight For Your Next  International Trip Planning Needs

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Frequently Asked Questions About ETPs

1. Why is the ETP  important for long-haul flights?

The ETP is important for long-haul flights because it helps expedite decision-making and enhance safety in the event of an in-flight emergency. Knowing the ETP helps pilots decide whether it will be faster to continue to the destination airport or re-route to an alternate airport if a diversion is necessary. This enhances both safety and operational efficiency. 

2. Do flight planning tools and apps like ForeFlight have ETP calculators?

Yes, flight planning tools like ForeFlight include automated ETP calculations, assisting with more efficient and accurate ETP planning. 

3. Do you need to file ETPs along with your flight plan?

No. ETPs are not required  when filing a flight plan. However, including them in flight plans, particularly for oceanic crossings or flights over remote areas, is considered best practice.