How high can I fly?

Set a legal altitude for the flight you are about to make, including flights near tall structures, and know what the altitude your control station displays actually measures.

• You know the height of the terrain under your route, not just of your take-off point. CAR 901.25
• You know whether there is a building or structure near your flight path, and how far from it you will be.
• You know which certificate you hold: the altitude limits apply to a VLOS operation, and exceeding them otherwise needs an SFOC. CAR 901.25

The base limit is 400 feet (122 m) AGL. "AGL" means above ground level — the height of the terrain directly beneath the aircraft, not its height above sea level and not its height above your take-off point. CAR 901.25

That distinction has a practical consequence in hilly terrain: flying at a constant barometric altitude over rising ground can put you above 400 ft (122 m) AGL without any change to the number on your controller. CAR 901.25

There is a second, separate allowance. You may fly up to 100 feet (30 m) above a building or structure, but only if the aircraft is within 200 feet (61 m), measured horizontally, of that structure. CAR 901.25

Read those two numbers together, because they are a pair. The 100 ft (30 m) allowance is tied to the 200 ft (61 m) horizontal proximity — it is not a general "fly 100 ft higher" permission. CAR 901.25

Both limits are subject to one override. A special flight operations certificate — RPAS permits operation above them. CAR 901.25

Note the structure of the section: subsection (1) sets the limits, and the words "Subject to subsection (2)" in the opening line tell you the limits are qualified from the start. Learning the limits without learning the qualification is a reading error the exam is designed to catch.

Traditional aircraft fly by reference to altitude above sea level (ASL). An RPAS usually displays altitude above ground level (AGL) measured from the launch site, and the gap between the two can be a few feet or as much as several thousand feet — so which one is on the screen matters. AIM 3.2.13

The AIM's own example makes the size of that gap concrete. An operation limited to 400 ft (122 m) AGL over Calgary is at approximately 4 000 ft (1 219 m) ASL, because the Calgary airport sits at 3 600 ft (1 097 m) ASL; near Tofino, where the airport is at 80 ft (24 m) ASL, the two numbers nearly agree. A pilot monitoring ATC radio frequencies hears altitudes in feet ASL that will look wrong against an AGL display. AIM 3.2.13

Because many RPAs reference their AGL altitude from the point of launch, the AGL height has to be inferred as the aircraft travels over uneven ground. Where the ground level changes a great deal and the flight runs near the 400 ft (122 m) limit, the AIM says a buffer may need to be included so the allowable maximum altitude is not exceeded. AIM 3.2.13

The instrument has its own error. An RPA's GPS receiver typically needs a clear view of a minimum of four satellites, and poor satellite geometry, reception masking by obstacles, or atmospheric interference can put the position and altitude it calculates out by up to 75 ft (approx. 23 m). AIM 3.2.13

Your maximum altitude depends on where you are flying:

Situation	What applies
Open ground, no structures nearby	400 ft (122 m) AGL CAR 901.25
Within 200 ft (61 m) horizontally of a structure	Up to 100 ft (30 m) above that structure CAR 901.25
Either limit, with an SFOC-RPAS	Limits may be exceeded per the certificate CAR 901.25
High terrain under a constant indicated altitude	AGL height rises even if your reading does not
Which altitude does my control station show?	Usually AGL from the launch site, not ASL AIM 3.2.13
400 ft (122 m) AGL over Calgary is roughly what ASL?	About 4 000 ft (1 219 m) ASL, because the airport is at 3 600 ft (1 097 m) ASL AIM 3.2.13
How far out can the displayed GPS altitude be?	Up to 75 ft (approx. 23 m) from geometry, masking or atmospheric error AIM 3.2.13

Warning The 100 ft (30 m) structure allowance is measured horizontally from the structure. It applies while you are close to it, not while you are near it on a map. Beyond 200 ft (61 m) horizontal distance, the 400 ft (122 m) AGL limit is the only one that applies. CAR 901.25

Symptom	Likely cause	What to do
You were legal at take-off but are unsure later in the flight	Terrain rose under a constant barometric altitude	Re-check AGL, not your indicated altitude CAR 901.25
You flew 100 ft above a building 240 ft away	The allowance only applies within 200 ft (61 m) horizontal	Stay within 200 ft, or return to the 400 ft (122 m) limit CAR 901.25
You need 500 ft for a survey	The limits are the default, not absolute	An SFOC-RPAS under 903.03 permits exceeding them CAR 901.25
You are unsure whether a particular structure counts	The section does not distinguish types	Treat any building or structure as covered
An ATC altitude sounds far too high	Traditional aircraft use ASL while the RPA display is usually AGL	Convert between the two before comparing AIM 3.2.13
The RPA reads the same height over ground that rises	AGL is referenced from the launch point and has to be inferred	Add a buffer when flying near the limit AIM 3.2.13
The displayed altitude is trusted to the foot	GPS altitude carries its own error	Allow for up to 75 ft (approx. 23 m) AIM 3.2.13

Practise: Maximum altitude Practise: Altitude types Practise: Altitude measurement

• CAR 901.25 — Maximum Altitude
• TC AIM, RPA chapter 3.2.13 — Maximum Altitude (types of altitude, and measuring altitude)
• Consolidation: CARs current to 2026-09-21

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中文译本： 我能飞多高？ — 非官方译本，仅供参考。