Ninety-One One Fifty-Five and the Cloud Clearance Rules Nobody Remembers Correctly

Under Federal Aviation Regulation 91.155, a VFR pilot in Class E or G airspace below 10,000 feet MSL during the day must have 3 statute miles of flight visibility and stay 1,000 feet above, 500 feet below, and 2,000 feet horizontally from any cloud. The exact numbers change with airspace class, altitude, and time of day - but the underlying logic never does: every value buys you time to see and avoid an aircraft you didn’t know was there.

Most pilots memorize one set of numbers, assume they’ve got the rule handled, and then fly into different airspace where everything changes. Here’s how the whole regulation actually fits together.

Why the cloud clearance rules change

The visibility and cloud clearance requirements in FAR 91.155 are not a single set of numbers. They shift based on three variables:

• What class of airspace you’re in
• Whether it’s day or night
• How high you are, measured both above the ground (AGL) and above sea level (MSL)

That’s the source of most confusion. The critical dividing line for altitude is 10,000 feet MSL - your altitude above the ocean, what your altimeter reads. Below it and at or above it, the rules differ significantly.

What are the VFR minimums below 10,000 feet in Class E?

For a general aviation pilot below 10,000 feet MSL in Class E airspace during the day, the numbers are 3, 1, 5, 2,000:

• 3 statute miles of flight visibility
• 1,000 feet above the clouds
• 500 feet below the clouds
• 2,000 feet horizontally from the clouds

Picture a cloud floating out there. You need to be a thousand feet over the top, five hundred feet under the bottom, or two thousand feet off to the side - and you always need at least three statute miles to see where you’re going.

A memory aid: treat the cloud like a building you don’t want to hit. Give it lots of room over the top (1,000 feet), because fast traffic can descend out of it. Underneath you need only 500 feet, because you can see what’s coming. And 2,000 feet to the side. Repeat “three, one, five, two thousand” until it’s automatic.

Why do cloud clearance rules exist at all?

The clouds are where instrument traffic lives. Aircraft flying under instrument flight rules (IFR) can be inside those clouds, flying purely on their gauges. They can’t see you, and you can’t see them until they burst out of the edge.

So the cloud clearance rule is really a time rule in disguise. It gives two aircraft - one who can see, one who can’t - enough space to avoid a collision when someone comes out of the white.

Consider an airliner descending at 250 knots that punches out of the bottom of a cloud layer. Tucked right against that cloud, you’d have a fraction of a second. Positioned 500 feet below and 2,000 feet to the side, you have room and time. That’s the entire point - collision avoidance written into law, not bureaucratic box-checking.

What are the VFR minimums at or above 10,000 feet MSL?

At or above 10,000 feet MSL in Class E, the rules change dramatically to 5, 1,000, 1,000, 1 mile:

• 5 statute miles of visibility
• 1,000 feet above the clouds
• 1,000 feet below the clouds
• 1 statute mile horizontally

Why bigger numbers up high? Speed. Below 10,000 feet, aircraft are held to a 250-knot speed limit under FAR 91.117. Above 10,000 feet, that limit comes off and aircraft move faster - so you need to see farther and stay farther from clouds to preserve the same reaction time. Faster airplanes, more space. The logic is consistent throughout the regulation.

What are the VFR minimums in Class G airspace?

Class G is uncontrolled airspace - usually near the surface out in the countryside, beneath the shelf of larger airspace. It carries the loosest rules in the system, and they change the most with altitude and time of day.

During the day, at or below 1,200 feet AGL in Class G, you need 1 statute mile of visibility and must remain clear of clouds. That’s it - one mile and clear of clouds, with no specific above/below/horizontal figures.

At night, at or below 1,200 feet AGL in Class G, the rules tighten back to 3 statute miles and the familiar 1,000 above, 500 below, 2,000 horizontal. The FAA looked at flying low and close to the ground in the dark and refused to extend the loose daytime allowance.

The night traffic pattern exception: if you’re within one-half mile of the runway in the traffic pattern, you may operate with 1 statute mile visibility and clear of clouds even at night, as long as you stay in the pattern. This exists so you can shoot night landings at a small untowered field, and it shows up frequently on knowledge tests. It’s a narrow carve-out - not an everyday habit.

Legal is not the same as safe

The daytime Class G minimum - one mile, clear of clouds - reads like permission and functions like a trap. It is legal, and it is also a superb way to fly a good airplane into terrain, a tower, or another aircraft scud running at the same one mile.

A minimum is the edge of the cliff, not the trail you’re supposed to walk. Good pilots have died perfectly legal. Every time you read a regulatory minimum, build extra margin on top of it with your own judgment.

The four scenarios to actually memorize

Don’t memorize the entire table. Memorize the handful of situations you actually fly:

1. Below 10,000 feet in Class E, day or night: 3, 1, 5, 2,000. Your bread and butter - know it cold.
2. At or above 10,000 feet MSL: 5, and 1,000 / 1,000 / 1 mile. Bigger, because everyone’s faster.
3. Low in Class G, daytime: 1 mile, clear of clouds - but treat it as the danger zone it is and give yourself far more room than the law requires.
4. Low in Class G at night: back to 3, 1, 5, 2,000, with the narrow traffic pattern exception.

Four scenarios organized the way your brain actually flies.

How does this show up on the checkride?

The Airman Certification Standards (ACS) place this in the airspace area of operations. The examiner wants you to state the basic VFR weather minimums for the airspace you’re actually planning to fly through - not recite the whole table like a robot.

The real skill they’re testing: look at your route, identify the airspace, and know whether the morning’s weather actually lets you make the flight - legally and safely.

Worked example: You plan a cross country. Your briefing reports a ceiling of 1,500 feet broken and visibility 6 miles. Your route stays in Class E, below 10,000 feet the whole way.

• You need 3 miles visibility. You have 6. Good.
• You need to stay 1,000 feet below the clouds. With clouds at 1,500 feet, that puts your legal ceiling at 500 feet AGL.
• Now the real question: do you want to scrape along at 500 feet over unfamiliar terrain to stay legal? Legal, maybe. Smart, no.

The regulation gave you a floor. Your judgment has to build the house on top of it.

Flight visibility vs. ground visibility, and statute vs. nautical

Two precision points that matter:

• Flight visibility is what you can actually see from the cockpit, and it’s what the regulation legally requires. The visibility reported at the airport (ATIS or weather observation) is ground visibility - your best proxy, but not what the reg is written around.
• Weather visibility in the United States is always in statute miles, while your airplane’s speed is in knots (nautical miles). Two different measuring sticks in the same cockpit - don’t mix them.

Key Takeaways

• FAR 91.155 minimums change with airspace class, altitude (the 10,000 feet MSL line), and day versus night.
• The everyday anchor is 3, 1, 5, 2,000: 3 SM visibility, 1,000 ft above, 500 ft below, 2,000 ft horizontal (Class E/G below 10,000 ft).
• At or above 10,000 feet MSL, minimums grow to 5 SM, 1,000/1,000, and 1 SM - because aircraft fly faster above the 250-knot limit.
• Class G daytime is loosest (1 mile, clear of clouds) but the most dangerous; night reverts to 3-1-5-2,000 with a half-mile traffic pattern exception.
• Every number exists to buy time to see and avoid traffic emerging from cloud. Legal is the floor; safe is your job.