How can people launch balloons privately (filled with helium or hydrogen) that reach the altitude of 30,000 feet? Isn't that a safety risk in the same way as geese?


6 Answers 6


Unmanned balloons can indeed create a safety risk for aircraft. An aircraft could collide with the balloon itself (as described in the case that Jan Hudec posted in his comment), or with the balloon's payload (see the FAA's AIM section 7-5-4 for general comments on this).

But it's important to note that unmanned balloons are (or should be) launched only after appropriate preparation and communication; most countries have some sort of regulations to follow. In the US (for example), 14 CFR 101 governs unmanned balloon launches and it includes the following requirements:

  • Launches must be in (mostly) clear skies and away from airports and built-up areas
  • The balloon must have a radar reflector and lights (if launched at night)
  • ATC must be informed in advance of the balloon launch, expected path etc.
  • The operator must track the balloon's position and descent and report them to ATC as needed

In other words, the balloon should be as visible as possible - both visually and on radar - and ATC should know where it is. That gives pilots a way to see and avoid the balloon and ATC can provide warnings and/or avoidance instructions to aircraft directly where possible, which is actually fairly similar to how aircraft avoid other aircraft.

Of course, there may be cases where someone launches a balloon without following those rules (or the local equivalents in another country). That would create a much higher safety risk but it would be illegal and the operator would be risking penalties for doing it.

  • 2
    $\begingroup$ This is a bit too specific to US regulations. $\endgroup$
    – os1
    May 25, 2016 at 16:36

High altitude balloons reach more like 30km rather than kft. This means that there's a limited time in which they can interfere with normal aviation traffic (which, during cruise, is usually in a fairly narrow band between 8-12km).

Outside of cruise can be more of a problem (i,e: When landing or taking-off). For that reason it's essential to launch from somewhere far from an airport, so that the balloon can ascend in a location where it will not affect air traffic. Most countries also require you to inform air traffic control in advance of a balloon launch so that they can issue a warning (NOTAM) to pilots that lets them know to be aware of balloon activity.

Lastly, one can reduce the risk to aviation by constructing the balloon payload carefully. The balloon itself doesn't pose much of a risk but a heavy/dense payload can. To reduce the risk lightweight components should be used and dense items like batteries kept to a minimum. Most countries also have rules governing the size and weight of the balloon that you can launch.

For balloons that can't meet the rules (too heavy, need to launch near an airport, etc) there's two choice: 1) Don't launch. 2) Perform a much more extensive risk analysis and actively divert air traffic away from the balloon. This requires air traffic control to be able to see the balloon (using a radar reflector or, more usually, a transponder). Because of the cost of this option it's normally only very important or high-value payloads that are sent this way (such as NASA's research balloons).


High altitude balloons going into commercial airspace that are large enough to be a threat to a plane require a NOTAM to be issued and even small balloon launches are encouraged to have a NOTAM. Also, a weather balloon will not spend very much time in the danger zone but will drift right through it, so the exposure is brief. Most commercial fights occur along well-known corridors and flight paths. Balloons are often launched far away from those lines of travel. Just that alone makes it pretty safe. Small planes do the same thing: stay away from commercial flight corridors.


As for the TAM flight, that does not sound like a High Altitude weather balloon. That sounded like an unmanned hot air balloon carrying a big banner. I am guessing, based on the article that it was designed to stay at a lower altitude so people could see the banner. High altitude weather balloons are like giant party balloons, very thin latex usually. They generally rise at 1000 ft/min and are out of busy airspace quite quickly. The payloads are limited to 12 lbs, but usually much lighter. Mine was just over 2 lbs. If the regulations are followed there is very little risk.

Good luck, do your research, and have fun.

  • 1
    $\begingroup$ Fascinating, Tom - say why don't you include some sort of telephone or something on the device which calls home when it lands and gives you the GPS location? (all that would cost like $10 these days, I'm sure adding only a tiny amount to the cost.) What's the deal on that? Cheers $\endgroup$
    – Fattie
    Mar 17, 2016 at 12:45

Also relevant: there are other considerations. Its generally acceptable to launch small experimental payloads (ie simple telemetry + call sign transmitter on a permitted ISM band) as long as the total uninflated weight is below the limit for a Class 1 drone ie <250g. The radar reflector must be a specified size and shape, connected to the balloon via something that can be readily detached in an emergency ie low melting point alloy + shielded nichrome U shaped cut-down and designed in such a way to prevent a hazard to anyone on the ground or in the air by limiting descent speed below 20fps. Ideally also with a hyperbright green LED integrated into the reflector to indicate its in descent phase if at night.

  • 2
    $\begingroup$ Welcome to Av.SE! Can you link to the source of these requirements so that those who are interested have the authoritative document & not only "an internet post" to work from? $\endgroup$
    – Ralph J
    Apr 24, 2021 at 19:37
  • $\begingroup$ Are pilots educated that a green light represents a descending object? $\endgroup$ Apr 25, 2021 at 12:25

How does one launch unmanned high-altitude balloons without posing a safety risk to aviation?

By using some common sense, and not relying entirely on the regulations to ensure safety.

In the US, FAR 101 governs free balloon operations. Note the requirement to notify ATC before launching.

One odd "loophole"-- it's arguably permissible to operate an unmanned free balloon in the surface-level Class E "extensions" (E3/E3a/E4 airspaces) that are adjoined to the inner core airspace areas of some airports for the purpose of protecting the instrument approaches. You'd want to use a great deal of caution, and only do so in good weather conditions, and only at airports that don't have scheduled airline service, since the scheduled airlines tend to use the instrument approaches regardless of the prevailing weather conditions.

The relevant FAR reads:

§101.33 Operating limitations. No person may operate an unmanned free balloon—

(a) Unless otherwise authorized by ATC, below 2,000 feet above the surface within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport;

Here are four FAA issuances that do not directly pertain to balloons per se, but that do construe that language like "within the lateral boundaries of the surface areas of... Class E airspace designated for an airport" does not include surface-level Class E "extensions" (E3/E3a/E4 airspaces):

  1. FAR 107.41 states

No person may operate a small unmanned aircraft in Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from Air Traffic Control (ATC).

A memorandum issued on January 8, 2018 by FAA staffer Scott J. Gardner, Acting Manager, Emerging Technologies, AJV-115, stated that according to the FAA's Airspace Designations and Reporting Points document, "The only type of Class E airspace that matches the language in 107.41" is E2 airspace. The memorandum stated:

In reviewing Class E Surface Area authorization requirements, we determined that the Class E authorization requirement only pertains to Class E surface areas for an airport, not the Class E extensions to Class D, C and E airspaces.

  1. This 2019 Power Point document entitled "Class E airspace", compiled by FAA Aviation Safety Inspector Kevin Morris for an FAA UAS (Unmanned Aircraft System) Symposium, contains graphics clearly indicating that no authorization is needed to operate an "unmanned aircraft" in surface-level Class E "extensions" (E3/E3a/E4 airspace), despite the language of FAR 107.41.

  2. The FAA's LAANC system for authorizing flight of Small Unmanned Aircraft under FAR 107 (and also under the October 2018 44809 Recreational Exception for limited (hobby) recreational operations of unmanned aircraft, which uses the same phrasing as FAR 107.41) does not include any surface-level Class E "extension" airspace (E3/E3a/E4 airspace) in the "gridded" airspace where authorization may be requested, thus implying that no authorization is required to operate a Small Unmanned Aircraft System (sUAS) or hobby model airplane, drone, etc in this airspace under the terms of FAR 107 or the October 2018 Recreational Exception.

  3. FAR 91.157(a) reads

"(a) Except as provided in appendix D, section 3, of this part, special VFR operations may be conducted under the weather minimums and requirements of this section, instead of those contained in § 91.155, below 10,000 feet MSL within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport."

This related ASE answer provided a (circa) 2010 response from the FAA ATO Western Service Center addressing the question of whether "Special VFR" operations may be conducted in surface-level Class E "extensions". The FAA ATO Western Service Center's response contained the following passage:

Our opinion is that E4 airspace is not part of the airspace designated as the surface area for an airport. The surface area for an airport is D, C, or E2. Extensions are treated differently from surface areas designated for an airport, ie there is no communication requirement. In addition extensions, by definition in 7400.9, are not airspace designated as the "surface area for an airport".

  • $\begingroup$ Yes, the regulations around the "extensions" are a real "train wreck" of ambiguity... $\endgroup$ Apr 24, 2021 at 18:53

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .