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Just missed a PPL written exam practice test question that asked me what the minimum safe altitude was over areas "other than congested areas". I chose "An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface."

It turns out this is the answer to the question for the area of flight called "Anywhere". The answer for the area of flight called "other than congested", however, is "An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure."

I can now handily regurgitate the correct answers on the written exam for either stated scenario/area. However I'm wanting to know, is the FAA trying to tell me something here? What is the difference between "other than congested" and "anywhere"? Is "other than congested" presumably more congested than "anywhere"? Anything to take away from this hair splitting other than grumbling about the FAA?

FAR 91.119 is as follows:

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface. Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft. Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

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    $\begingroup$ I was taught that "congested area" was the area on a sectional that is yellow, meaning enough lighting to light it up at night. This definition may be apocryphal however. $\endgroup$ – rbp Jul 17 '16 at 16:59
  • $\begingroup$ @rbp I used to think those were just municipally incorporated areas, but after just now looking at the city limits of Spartanburg, SC (whose county is mostly unzoned and unincorporated but fairly populous) compared to the yellow outlined area on the sectional, the sectional's yellow Spartanburg area takes up more area than the city limits. So maybe there is something to that. $\endgroup$ – boulder_ruby Jul 17 '16 at 17:11
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The difference is subtle, but here it is:

anywhere means anywhere: At all times you need to operate at an altitude where, should you lose power, you can put your aircraft on the ground without "undue" hazard to anyone on the ground.
Ignoring all airspace considerations, say you're operating over a city (a congested area), and keeping to the bare minimum requirement for altitude and distance from obstacles. Your engine now fails, and your only "landing" options all involve slamming nose-first into the side of a building. You were not operating "at an altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface".
Since we all want to be able to make safe emergency landings this rule is largely common sense with the force of regulation.

other than congested areas is stuff like farmland or open beaches: you COULD operate much lower and closer to obstacles here and still be within the rules above (you're 300 feet AGL over an open field with a barn 300 feet to your right -- The engine dies, you set it down in the field, and everything is cool), but the FAA (and Farmer Brown in the barn milking Bessie) would prefer you not be that close to the barn in the event of say a flight control malfunction. Most pilots also wouldn't want to be that close to the barn at that low an altitude (unless engaging in an approved aerobatic demonstration with appropriate waivers) anyway, so it's usually a non-issue.

That leaves congested areas - cities, suburbs, crowded beaches, etc - where the FAA bumps up the minimum obstacle clearances / altitudes for the comfort and safety of folks on the ground.
One could contrive a scenario where you could safely fly at 1500AGL next to a 2000-foot building (like a long, clear, mostly-empty park adjacent to it that you could fly over & use for the "anywhere" emergency landing requirement), but again if something else went wrong you might go into the side of the building. As there are more people in "congested areas" to be freaked out by an airplane flying at a safe-but-rather-close distance, and more people who could be hurt by an unexpected departure from controlled flight, the margins are increased to provide a higher minimum level of safety.
As with Bessie in the barn, most pilots probably don't want to be this close to buildings full of people (and the associate mechanical turbulence), and while circling your friends house in the suburbs is fun it doesn't have to be done low enough to pick out the individual bricks in their driveway and you really should be high enough to land on their street safely if your engine quits, which these minimums will likely allow.

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    $\begingroup$ There are really three categories, congested areas, other than congested areas, and under that, the sub-category, open water or sparsely populated areas. I'm not going to get into the nuances of what congested is or is not, but it is worth noting that the FAA considers other than congested areas to include areas that are more heavily populated than merely open water or sparsely populated areas. $\endgroup$ – J Walters Jul 19 '16 at 11:32
  • $\begingroup$ @JonathanWalters Yeah, the FAA's definitions are kinda weird - open water or sparsely populated areas is really a subclass of "other than congested areas". I've always interpreted open water/sparsely populated to carve out what I call a Lindbergh exception -- "That one boat in the middle of the blue ocean" or "That one house in the middle of the desert" that you can't get closer than 500 feet from while you're skimming the surface in ground effect so you don't run out of fuel on your distance-record-setting flight. $\endgroup$ – voretaq7 Jul 19 '16 at 16:24
  • $\begingroup$ @voretaq7: How sparsely-populated is "sparsely populated"? $\endgroup$ – Sean Apr 7 at 3:31
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It probably makes sense to state that this regulation will have some variances in different countries.

In the UK, when I sat my pilot exam in 2000, aircraft are only allowed to fly below 500 ft during take off, landing, whilst ridge soaring(gliding aircraft only) and to avoid low cloud.

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