Definition
Takeoff weather minimums (visibility and sometimes ceiling) that are higher than, or otherwise different from, the standard minimums established by regulation for an IFR departure at a particular airport. They are published when terrain, obstacles, or other local factors require better visibility or specific climb gradients to depart safely. Nonstandard takeoff minimums are indicated on instrument approach charts by a small triangle symbol containing the letter T and are detailed in the front of the Terminal Procedures Publication.
Plain English
These are special weather rules for taking off on an instrument flight plan from certain airports, where you need clearer weather than usual before you are allowed to depart. The airport has something nearby — like hills, towers, or terrain — that makes a normal departure unsafe in low visibility, so the FAA raises the bar.
Context Anchor
A pilot sees these during an IFR preflight briefing, on departure information for an airport, or when reviewing instrument procedure notes before takeoff.
Derivation
Nonstandard simply means 'not the standard one.' Here, 'standard' refers to the default IFR takeoff minimums set by regulation (typically 1 statute mile visibility for aircraft with two engines or fewer). When an airport's published minimums differ from that default, they are nonstandard.
Why Pilots Care
Pilots must know these modified limits to avoid obstacles and meet legal requirements for a safe IFR departure.
Intuition Check
Do not read “minimums” as just a suggestion or comfort level. Here it means the lowest published condition or performance used for that IFR takeoff; “nonstandard” means the normal default does not apply.
Example Sentence 1
Before filing IFR out of that mountain airport, the pilot checked the chart and saw the T-in-a-triangle symbol, indicating nonstandard IFR takeoff minimums.
Example Sentence 2
Nonstandard IFR takeoff minimums at the mountain airport delayed the departure until conditions improved.