When flying from Florida to the north east (and visa versa), many aircraft stay over land and basically follow the coast line. Others take a more direct route and cut over the Atlantic ocean. I thought this maybe had something to do with ETOPS, but I am curious if anyone knows why some route over the ocean, and some over land. At any given time, it could be the same carrier and even the same type. For example, there could be two Delta A321's headed to FLL. One is flying over the ocean, and the other skirting the coast line. Any explanations as to why? I thought they would all follow the most direct efficient route as possible?

A direct route from MIA to BOS would require rafts and vests, but not ETOPS, though the regularly used airways would tend to keep you a bit closer. While I think the mainline carriers have gone to rafts and vests on most of all of their fleet, there could be oddballs out there. Additionally, the routes up and down the east coast are heavily trafficked and may simply require aircraft to fly different routings. Further, if the aircraft has a MEL for something, that may affect their ability to accept an extended over water routing.

Another factor, and one that doesn't get talked about as much, is the airlines having preferred routes that they always file. For example, every AA flight today is taking the same routing from BOS to MIA - hugging the coast. DL's flight to MIA is going further out on a routing about 50 nm shorter. Depending on winds and how they get vectored off the arrival and onto the approach, 50nm can easily be a rounding error or even quicker.

The Airspace


The highlighting generally shows the three different types of northeast-to-Florida (and vice versa) routes. Note that the term route can generally be used interchangeably with airway.

• The blue highlight (1) shows the inland routes. These are often congested, especially since non-overwater equipped aircraft are not capable of using the next two types of routes. The Northeast Corridor (NEC) project has removed all jet routes and replaced them with Q routes over the past several years. Most of these Q routes are unidirectional for more efficient traffic flows to and from Florida.

• The yellow highlight (2) shows the "AR" routes. These routes are used extensively by overwater-equipped aircraft and are often the most efficient routes between the northeast and eastern Florida. Aircraft generally must be overwater-equipped to use these routes. Many, but not all airliners are overwater-equipped. For all aircraft/operators that I am aware of, the AR routes do not require ETOPS, as they are all within 60 minutes of an adequate airport (a 60 minute radius around adequate airports defines ETOPS vs non-ETOPS airspace - the distance that equals 60 minutes varies by aircraft/operator). The term "AR route" comes from the previous airway designation: just as jet airways begin with J (e.g. J64), the airways within the yellow highlighted area were termed "Atlantic Routes" and began with AR (e.g. AR21). As of this year, the airways themselves have been co-designated as Y routes (e.g. Y319), but the general airspace (the yellow highlighted area) is still generally referred to as the AR routes.

• The red highlight (3) shows the "WATRS" route. This is used much less often than the inland and AR routes, but it serves a purpose. Obviously, it take more time and fuel to use than the inland and AR routes. Generally, the WATRS route is used during periods of high congestion, such as right now during the holiday season and more generally during the "snowbird" season when north-south travel along the east coast is busiest. When the WATRS route is used, it is often only during the day, since east coast traffic volume decreases significantly at night. The WATRS route can only be flown by overwater-equipped aircraft, but it is not an ETOPS route (barring any strange aircraft/operator case that I'm not aware of). The advantage to using it is removing traffic volume on the other two route structures and, for an individual flight, reducing or avoiding delays that may be incurred by planning on the other two route structures during times of high demand. In some cases, the extra enroute time on the WATRS route more than offsets the delay that a flight would have to take prior to departure waiting for a "slot" on the inland or AR routes. WATRS stands for Western Atlantic Route System, which is essentially everything including and east of the red highlighted area. The highlighted route is called WATRS because it is only route structure (of these three) to enter New York Oceanic (i.e. WATRS) airspace. The other two route structures remain in the domestic centers' airspace. As a note, the route used to be called AZEZU (named after a specific waypoint on the route), but was renamed WATRS last year.

You'll notice some gaps between the highlighted areas. These are warning areas, which is a type of special use airspace (SUA) that is often reserved for military use. When these warning areas are active (which occurs on most weekdays and some weekends), non-military flights are generally not cleared into them. Therefore, the route structures have to avoid this airspace. This particularly affects the WATRS route, which must proceed well east before turning back south/southwest to join the AR route structure into Florida.

Reasons For Using The Route Structures

• The AR routes (yellow highlight) are the most direct routes between the northeast and Florida. They are often the quickest/most efficient and are used more often than not by airlines and overwater-equipped GA. The inland routes are usually the first to become saturated with traffic, and overwater-equipped aircraft are then encouraged to file on the ARs to reduce traffic volume inland. Since the northeast corridor (in part, the airspace between Florida and the northeast) is some of the most congested in the world, it is important to spread flights out between different traffic flows (in other words, spreading them out over the highlighted areas) in order to ensure no one area is oversaturated with traffic, leading to extensive delays.

• The inland routes (blue highlight) are used for all types of traffic, and must be used by non-overwater equipped aircraft. They are the first to become saturated with traffic, as airline traffic mixes with GA and numerous complex arrival and departure flows into the major northeast and Florida airports. On busy days, ATC can issue traffic management initiatives such as miles-in-trail (MIT) and airspace flow programs (AFPs) that help to "meter" (i.e. space out) traffic. The inland routes are the most susceptible to this, especially on the east coast of Florida where the majority of the traffic is. These traffic management initiatives can lead to delays and encourage capable aircraft to use the AR or WATRS routes.

• You may ask why capable aircraft don't always just file on the AR routes because they are more direct and less prone to congestion and delays. In fact, on most days where weather isn't a factor, airlines will usually file the ARs with their capable aircraft, even if it does end up being slightly less efficient due to winds. However, both winds aloft and other weather (namely, thunderstorms and turbulence) play a factor in route selection. On some days, a weather system or the jetstream can cause a significant difference in wind direction and speed on the ARs and inland routes. Consider a southbound flight from New York to Florida. While more direct, the ARs may have a slight headwind while the inland routes have a significant tailwind due to a low pressure system in the area. This may cause the inland route to actually be quicker and more efficient due to the difference in wind component. Thunderstorms and turbulence are also frequent visitors to the east coast and will often dictate the selection of one route over the other, even at a slight disadvantage in enroute time/fuel burn.

• The red highlighted WATRS routes are not often used outside of the high traffic volume situations mentioned before. In some rare cases where a hurricane or other major convective system is parked near the east coast, a WATRS route may be used. However, WATRS route usage is almost always for traffic reasons. For example, the current holiday period means very high traffic volume. Almost daily, a modified version of the WATRS route is recommended to move as much traffic as possible off of the congested inland and AR routes. In exchange for a longer enroute time and more fuel burn, operators using the WATRS route are usually exempt from any inland/AR delays that are common at this time of year.

• Along the east coast, ATC often publishes "reroutes," which are either recommended or mandatory routes for aircraft either going between two regions/airports or flying through a specific piece of airspace. Given the somewhat random nature of route distribution (i.e. at a certain time of day, many aircraft can be going through one small area while other airspace is uncongested), ATC sometimes has to put flights on defined routes to separate them. Instead of a "jumble" of flights through a particular area, ATC may elect to put all of the Washington D.C.-area to Florida flights on one inland airway, the New York to Florida flights on another inland airway, and recommend the AR routes for Boston-area to Florida flights. This effectively creates three major "flows" of traffic down the northeast, making it easier to manage and removing "clumps" of flights. The remainder of flights not falling into those example categories can file whatever they like, but much of the traffic volume has been organized into separate flows.

• The reason you'll see the same operator and even the same aircraft type using different routes is usually for the reasons above. One flight may be caught up in a potential inland delay and decide to use the AR routes to reduce the delay. The next flight (same operator and same aircraft type) may be leaving just late enough that the inland delay no longer applies and the flight decides to file inland in order to avoid turbulence reported on the AR routes. At the airlines, even if two flights appear related (same city pair, same aircraft type, same day), two different people likely planned the flights. Slight differences in winds aloft, weather, and aircraft capabilities (maybe one individual aircraft has its overwater equipment removed/deferred) can dictate different routes. Even staffing in the different ATC facilities along the east coast can result in one route being more favorable than the others.

dctraynr wrote:

You'll notice some gaps between the highlighted areas. These are warning areas, which is a type of special use airspace (SUA) that is often reserved for military use. When these warning areas are active (which occurs on most weekdays and some weekends), non-military flights are generally not cleared into them. Therefore, the route structures have to avoid this airspace. This particularly affects the WATRS route, which must proceed well east before turning back south/southwest to join the AR route structure into Florida.

Thanks for the comprehensive response. AR and WATRS routes what FAA refers to as "water" and "deep ocean" in the Prefs database?

Cubsrule wrote:

dctraynr wrote:

You'll notice some gaps between the highlighted areas. These are warning areas, which is a type of special use airspace (SUA) that is often reserved for military use. When these warning areas are active (which occurs on most weekdays and some weekends), non-military flights are generally not cleared into them. Therefore, the route structures have to avoid this airspace. This particularly affects the WATRS route, which must proceed well east before turning back south/southwest to join the AR route structure into Florida.

Thanks for the comprehensive response. AR and WATRS routes what FAA refers to as "water" and "deep ocean" in the Prefs database?

It depends on the facility, but for the most part, yes. The "water" remark is usually referring to the AR routes and "deep water" usually refers to either the red highlight WATRS route or another route "deeper" into New York Oceanic airspace.

dctraynr, thank you for the amazingly detailed response! It is fascinating how much detail does into this. I really learned a lot from your post, much appreciated!