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According to FAA regulations, how far should a commercial jet be away from another plane in-flight?

commercial jet img

How about military planes? They get really close when in formations... Is there a minimum distance?

Military formation img

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formation flight is a different beast than normal individual flights –  ratchet freak Mar 27 at 11:38
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In the 2nd picture, though the planes appear very close to each other, but that is because of the picture. In reality, planes flying in formations like this do not flight exactly on the same level. For example, see this picture, the planes following are higher. –  Farhan Mar 27 at 13:38
    
@Farhan Not always true. There are different formations used in different scenarios, and sometimes vary to accomodate aircraft-specific characteristics. Some patterns with some aircraft are same-level. (Not necessarily in that particular picture though.) –  dvnrrs Mar 27 at 15:00
    
Check out this Episode of Air Crash Investigation. It is about a mid air collusion caused by pilots not following ATC's directions. Though the crash took place on non US soil there is some information about flight separations during cruise and approach. –  caffinatedmonkey Mar 27 at 15:15
    

3 Answers 3

up vote 31 down vote accepted

The question specifically asks about FAA regulations, so I will try to provide specific citations.

Summary

For a commercial airliner (as the question asked), separation will usually be at least 3 miles laterally, or 1,000 feet vertically. In the enroute environment, far from radar antennas, a 5 mile rule is applied laterally. This is true in most but not all situations. There are exceptions: see below.

Note also the "or": it is allowed (and in fact rather common) for two jets to cross paths at the same moment, with one 1,000 feet directly above the other. The 3 miles is only required if the jets do not have at least 1,000 feet of vertical separation.

Pilots

The regulations do not set a specific distance that pilots flying under VFR must maintain from each other. There's just the following blanket statement:

§91.111, Operating near other aircraft: (a) No person may operate an aircraft so close to another aircraft as to create a collision hazard. (b) No person may operate an aircraft in formation flight except by arrangement with the pilot in command of each aircraft in the formation.

In addition, there is the catch-all "careless or reckless operation" clause:

§91.13, Careless or reckless operation: No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.

Pilots flying under IFR are subject to the same kinds of rules, and are still responsible for maintaining separation from other traffic when in visual conditions. The rules are the same: the pilot is given the discretion of deciding what a "safe distance" is.

Actual distance limits only come into play for the air traffic controllers, who are responsible for providing minimum separation distances between IFR traffic.

Air Traffic Controllers

The set of FAA regulations for air traffic controllers is FAA order 7110.65. These regulations are quite complicated and there are lots of exceptions and corner cases for various scenario. I'll try to give only the most basic rules here, but note that a full reading of 7110.65 would be necessary to understand all the minutiae.

Vertical separation:

Lateral separation:

  • 5-5-4 Minima. In general, 3 miles in the terminal environment and 5 miles in the enroute environment (with exceptions).

Things get more complicated in the following scenarios, and exceptions apply to them:

For these scenarios the regulations are rather lengthy and complicated, so I would simply refer you to Order 7110.65 in general.

Military

When flying in airspace controlled by ATC, military pilots must follow the same rules as civilian aircraft. ATC will keep them separated according to the rules above. However, there are two main exceptions to this.

When flying in formation, such as for training, aerial refueling, or intercepting aircraft, they are much too close for ATC to provide safety. In these cases, ATC will allow the pilots to fly under MARSA (Military Assumes Responsibility for Separation of Aircraft). In the case of interception, if the fighter pilot is not able to see the aircraft they are intercepting before the minimum separation, they must break off. They can only fly under MARSA if they can actually ensure visual separation.

The FAA can also define an MOA (Military Operations Area). Once military aircraft enter this area, ATC is no longer responsible for them and they are under MARSA. When the aircraft leave the MOA, ATC resumes control. They can still be under MARSA for a formation, but ATC will keep that formation separated from other traffic.

In tactical formation flying, there is no limit. The Blue Angels routinely fly with only 18" separation between the wing tip and the cockpit canopy. Combat aircraft fly a variety of different formation patterns at varying distances, and pilots are extensively trained on each pattern and what the appropriate/safe distances are. (For example, a fingertip formation allows for much closer flying than a line-abreast formation.)

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Excellent answer! I would suggest adding a paragraph about visual separation between aircraft since it is a commonly used procedure. I would also suggest making it more clear that the 1,000 ft separation is for IFR-IFR traffic. It is common for IFR-VFR to have 500 ft separation because that is how the "normal" flight levels are setup. –  Lnafziger Mar 27 at 17:07
    
I believe the part about military only applies to US and the rules are very different in different countries. –  Jan Hudec May 11 at 15:31

With formation flights it is as close as the pilots feel comfortable with in the circumstances. On clear days and in level flight brushing wingtips is allowed as long as you don't endanger the other planes.

For normal (commercial) flights vertical separation of 1000 feet is maintained when passing each other.

for planes incoming for landing there is 4-8 NM radar separation depending on the size and weight of the planes.

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you have 3 separations for commercial flights

  1. vertical separation: two aircrafts flying in the same direction will be separated by 2 flight levels (FLs), equivalent to 2000 ft. The intermediate FL is occupied by planes flying in the opposite direction. Each aircraft has thus 500 ft above and below the assigned altitude of free airspace.

  2. lateral separation: the airways are defined as being 10 nautical miles wide, 5 for each side

  3. longitudinal separation: I have no detailed information on this for the cruise, I hope someone else can fill the gap. During approach it depends on the size of the preceding aircraft.

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you can write an entire book on longitudinal separation and still not be done with it: depending on whether it is radar or procedural separation, VOR, DME, Mach number tehnique, cruise or approach service. About 10 minutes or 80NM for cruising and between 2 to 6 mins or 5NM to 2.5 NM on approach is a good rule of thumb –  Radu094 Mar 27 at 12:41
    
@Radu094 Lol, absolutely true. In fact an entire book has been written about it... FAA Order 7110.65 :) –  dvnrrs Mar 27 at 16:21

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