KSEA — Seattle–Tacoma International Airport

Runway numbers = magnetic heading

A runway's number is simply its magnetic heading rounded to the nearest 10°, with the last zero dropped. So Runway 09 points about 090° (east) and Runway 27 points about 270° (west) — the same strip of pavement, two directions 180° apart. An L / R / C suffix only tells parallel runways apart and has nothing to do with the heading.

Headings shown are derived from the runway number (number × 10) and are approximate; the painted number can differ slightly and shifts over time as magnetic variation changes.

Is this airport towered? What airspace?

A control-tower (TWR) frequency is published here, so this is a towered airport — you need a clearance to take off and land while the tower is open.

Here's the method to figure out the airspace: a tower usually sits inside Class B, C, or D surface airspace, while a non-towered field is typically surrounded by Class E or G. That's the general rule, not a guarantee.

We don't publish a verified airspace class for this field, so don't take the rule above as fact — confirm the exact class (and its dimensions) on the current VFR sectional chart or in the Chart Supplement before you fly.

Decode the frequencies

These are the radio services published for KSEA. Knowing who's on the other end — and when to use each one — is exactly what the written exam asks:

• Approach / Departure (A/D) — Approach / Departure Control — the radar facility that sequences and separates traffic arriving to and departing from the terminal area around the airport.
• Clearance Delivery (CLD) — Clearance Delivery — issues your IFR (or VFR flight-following) clearance before you taxi, so the tower and ground frequencies stay clear.
• CTAF (CTAF) — Common Traffic Advisory Frequency — at a non-towered field, pilots self-announce position and intentions on this shared frequency. There is no controller; you are talking to other traffic.
• Ground (GND) — Ground Control — controls aircraft taxiing on the movement area (taxiways and ramps) between the runway and parking.
• Tower (TWR) — Tower — the air traffic controller who clears you to take off and land and sequences traffic in the surface area. Its presence is why this is a towered airport.
• UNICOM (UNIC) — UNICOM — a non-government advisory station (often the FBO) for airport advisories like the favored runway, plus services such as fuel. Frequently the same frequency as the CTAF.

Density altitude right now

Density altitude is the altitude the airplane performs as if it were at — your pressure altitude corrected for temperature. On a hot day, or at a high airport, the thinner air pushes density altitude up, which lengthens the takeoff and landing roll and weakens climb. We can calculate it live here whenever KSEA is reporting a current METAR (we need temperature and an altimeter setting).

Traffic pattern altitude

The standard traffic pattern for light aircraft is flown 1,000 ft above the field. With this field at 433 ft, that's an estimated TPA of 1,433 ft MSL.

Standard light-aircraft pattern is 1,000 ft above field elevation, but the actual TPA varies by airport — always confirm it in the FAA Chart Supplement.

Radio-out at a towered field? Watch for ATC light-gun signals: steady green = cleared to land (or cleared for takeoff on the ground), flashing green = return to land / cleared to taxi, steady red = give way / stop, flashing red = unsafe, do not land / taxi clear of the runway, flashing white = return to starting point, alternating red-and-green = exercise extreme caution.