What are SRS and LAHSO categories?
You'll see two numbers on aircraft spec sheets that don't get much attention: SRS category and LAHSO category. Both come from the FAA. They solve different problems, but they're both about what happens near the runway.
SRS - same runway separation
Think of it this way. A B747 comes in at 155 knots. A Cessna 172 approaches at 75 knots. If the Cessna follows the 747, the gap between them grows on its own - the 747 pulls away. If the 747 follows the Cessna, it's going to eat up that spacing fast.
SRS categories sort aircraft into buckets by approach speed:
| Category | Speed range | Who's in here |
|---|---|---|
| 1 | Under 91 kts | Cessna 150, Piper Cherokee |
| 2 | 91-120 kts | Cessna 172, Bonanza, King Air |
| 3 | 121-140 kts | B737, A320, E175, CRJ-900 |
| 4 | 141-165 kts | B777, B747, A330, B787 |
| 5 | Over 165 kts | Concorde (retired) |
Category 3 is where most airline traffic lives. That's your 737s, A320s, and regional jets.
The numbers matter for sequencing. When you put a Cat 4 behind a Cat 2, the faster aircraft closes on the slower one throughout the approach. The controller needs enough initial spacing to keep things safe until both are on the ground. Conversely, a Cat 2 behind a Cat 4 is easy - the gap opens naturally.
LAHSO - land and hold short operations
LAHSO is a different animal. Sometimes an airport has two runways that cross each other. During LAHSO, one aircraft lands on a runway and stops before reaching the intersection point, while another aircraft uses the crossing runway at the same time.
Not every aircraft can do this. A Cessna can stop in 2,000 feet. A B747 needs 6,000+. The LAHSO category reflects how much runway an aircraft needs to stop:
| Category range | What it means | Typical aircraft |
|---|---|---|
| 1-3 | Stops short, no problem | Light singles, small turboprops |
| 4-6 | Moderate stopping distance | Regional jets, small narrowbodies |
| 7-9 | Needs most of the runway | B737, A320, larger narrowbodies |
| 10+ | Uses the full runway | Widebodies - B777, B747, A380 |
Higher number = needs more pavement. The controller checks if the available distance before the hold-short point is enough for that aircraft's category. If it isn't, LAHSO can't be offered.
Pilots can always refuse LAHSO regardless of the aircraft's category. Wet runway? Gusty crosswind? Just don't feel like it today? All valid. ATC has to have a backup plan ready.
In radarcontrol.io
Both categories appear on aircraft reference pages in the Equipment section. They're sourced from the openScope database.
The sim doesn't currently simulate LAHSO operations (no intersecting runway procedures). SRS categories are used in approach spacing calculations when sequencing arrivals to the same runway.
Related: What are aircraft categories? | What is RECAT? | How arrivals are sequenced
Guides: Arrivals guide | Aircraft types