intro
Sea-Tac Airport is a busy Class B airport that serves the Puget Sound region. This guide is meant for pilots who may not have been before and want a bit of a heads up on what to expect.
geography
Seattle is located on Puget Sound about 80 nm inland from the Pacific Ocean. To the east are the volcanic Cascade Mountains and across the water to the northwest are the Olympics. Much of the region was shaped by glaciation, leading to lots of drumlin hills with a north-south orientation. Sea-Tac Airport is built on one of these hills with north/south runways that has some fill added on the west side.
Weather
Cloudy: typically southerly winds and stratiform clouds with “Seattle Sunshine” (i.e. drizzle). Expect the 16s. Cold fronts are common in the winter, which means bumpier southwesterly winds and likely icing on the arrivals. Most of the clouds come in off the Pacific through the Chehalis Gap between the Olymics and Cascades. It’s often breezy in that region. The ATIS usually won’t have RCCs, so assume it’s 5/5/5 if there’s been drizzle.
Sunny: typically light northerly winds and warm weather, launching and landing on the 34s. In the winter with a tight dewpoint spread and light winds this can lead to lots of radiation fog overnight, so expect Cat II/III operations and significant flow delays in the mornings. The 16s have lower mins than the 34s, so expect 16s even if winds are slightly northerly.
Warm fronts are rare, but deserving of attention. They typically have a layer of dry air come over the Cascades before the clouds show up, leading to strong easterly winds. If you’re near your crosswind limitations, be aware that most airports in the region that can accommodate larger aircraft are oriented north-south due to the drumlin hill geography, so think carefully about alternates that might offer better alignment (Vancouver, Portland) or have crosswind runways (Pasco, Spokane). Anything close, like Paine Field (KPAE) or Boeing Field (KBFI), is likely to have the same crosswind problem.
Convective weather is uncommon, but when it happens you can expect frequent wind changes and consequently arrival/runway changes. Be on your toes.
Snow and freezing weather are likewise uncommon, so expect it to be a zoo and to get delays. The one time I got a double runway change was during snow. They gave us 16R, then swapped us 16L to plow 16R, and got done early and swapped us back to 16R right as we were about to turn base. Lots of twiddling in the box.
Sunny: typically light northerly winds and warm weather, launching and landing on the 34s. In the winter with a tight dewpoint spread and light winds this can lead to lots of radiation fog overnight, so expect Cat II/III operations and significant flow delays in the mornings. The 16s have lower mins than the 34s, so expect 16s even if winds are slightly northerly.
Warm fronts are rare, but deserving of attention. They typically have a layer of dry air come over the Cascades before the clouds show up, leading to strong easterly winds. If you’re near your crosswind limitations, be aware that most airports in the region that can accommodate larger aircraft are oriented north-south due to the drumlin hill geography, so think carefully about alternates that might offer better alignment (Vancouver, Portland) or have crosswind runways (Pasco, Spokane). Anything close, like Paine Field (KPAE) or Boeing Field (KBFI), is likely to have the same crosswind problem.
Convective weather is uncommon, but when it happens you can expect frequent wind changes and consequently arrival/runway changes. Be on your toes.
Snow and freezing weather are likewise uncommon, so expect it to be a zoo and to get delays. The one time I got a double runway change was during snow. They gave us 16R, then swapped us 16L to plow 16R, and got done early and swapped us back to 16R right as we were about to turn base. Lots of twiddling in the box.
airport layout
Sea-Tac has three parallel runways on a plateau with most of the ramps on the east side of the field. The western runway, 16R/34L is the shortest, so it gets most of the arrivals. Plan this unless you’re flying a heavy and you request 16L/34R. In any case, get landing numbers for both. 16C/34C is rarely used for arrivals, and is sometimes used for departures if there’s a long line. Plan departure numbers for the east and center runways just in case. Most departures and some heavy arrivals go to 16L/34R.
Arrivals
There are four commonly-used STARs going into Seattle, one from each corner. These are, clockwise from northwest, the MARNR, GLASR, CHINS, and HAWKZ. Each has a north/south flow. Approach often vectors you off the STARs for spacing and then merges the streams together on final, most commonly 16R/34L and less frequently 16L/34R for heavies or for the occasional runways change for smaller aircraft. If you’re on a downwind, you can expect them to either send you long or cut you in to fill a hole. I like to keep my map display wider (25 or 12.5 in the E175) and keep the extended TCAS on to see the stream of inbounds and guess where we’re going. If approach gives you “descend and maintain 5000,” you’re going further out, so delay your configuration to save fuel. “Descend and maintain 3000” is code for “We’re slam-dunking you into a hole, please hustle down ASAP and expect a base in 3…2…1….” If you see a hole, you can sometimes get it by offering “We can hustle down to 3000 and take an early turn.” If you see a nice long conga line with even spacing that’s 6 deep, you’re not getting a shortcut, so avoid the chatter and consider staying clean as long as possible to save fuel. In the base, expect to slow to 210, and plan 190 on long final, then 170 to the FAF. In the E175, I like to put 190/170 in the PERF approach speeds for Flaps 1 and Flaps 2, respectively. If you fly an airplane with a slow ref speed (<130 KIAS), try to be a good neighbor and configure later, where reasonable and safe, and plan an early exit so that the crew behind you doing 150-160 doesn’t get sent around. When approach gives you a join altitude, they expect you to maintain that until established. That’s because they might have traffic on the parallel joining at a different angle, so they separate them vertically to avoid traffic conflicts. Coming in to the 16s you may get asked to stay with approach until the FAF, then go to tower. That’s usually because there’s traffic below you on final at KBFI, so approach will want to be able to tell you to go around if someone at KBFI does.
MARNR
Named after the Seattle Mariners baseball team, this STAR comes in from the northwest. If you’re landing on the 16s, expect to get vectored for spacing around MARNR, usually heading 100-140 and 10000, then heading 070 and 7000, then 5000 to join the approach for 16R. Unless it’s really quiet, like early in the morning, you’re unlikely to get the transition from GRIFY onto the ILS, so I like to load the approach from AGANE with a discontinuity so that if they join us outside AGANE, we have the vertical protection already loaded in. In the rare exception case, it's easier to edit GRIFY->CELAK than to re-add AGANE. On the 34 side, expect vectors onto final and the occasional slam-dunk if a hole opens up.
GLASR
Named after Glacier Peak (do yourself a favor and avoid calling it “Glazzer”), you can expect vectors right after JAKSN toward the 16s, typically heading 230 or 240 down to 8000 or 7000, then down to 5000 to join. If it's busy, they may give you more of a dogleg like heading 270, then direct AGANE later, so don't be too eager to activate vectors-to-final. If approach wants you fast, go down first (FLCH) and be prepared to slow to 210 as you get close to AGANE. If it’s cloudy, expect icing in the descent as the clouds pile up on the western side of the Cascades. In the E175, plan to get normal and SPIS landing numbers. On the 34s, they sometimes leave you high or give you speed 210 further out on the downwind because they need the spacing. It’s often a good idea to grab some drag when they give you this to prevent ending up high. Again, watching the extended TCAS will help you plan.
CHINS
Similar to the GLASR, this one comes over the Cascades, but from the southeast. Prior to descent, check the winds aloft. If they’re 180-230 and >25 knots, you’ll be in the lee of Mt. Rainier and you should expect bumps in the descent. Help keep your teammates and passengers safe by giving them a heads up and seating them before that. Going to the 16s you can plan to descend at 250 to 5000, then 210 in the base. Going 34s, expect to get vectored 270 or 260 and dropped down to 8000 or 5000 a bit early. One threat to plan for when it’s nice out is GA traffic east of the Bravo shelf. If you see a bunch of targets on your TCAS, monitor 122.75 and listen for “Southeast Practice Area” calls. Every so often someone busts the Bravo, so don’t assume that you’re clear of GA there.
Named after the Seattle Mariners baseball team, this STAR comes in from the northwest. If you’re landing on the 16s, expect to get vectored for spacing around MARNR, usually heading 100-140 and 10000, then heading 070 and 7000, then 5000 to join the approach for 16R. Unless it’s really quiet, like early in the morning, you’re unlikely to get the transition from GRIFY onto the ILS, so I like to load the approach from AGANE with a discontinuity so that if they join us outside AGANE, we have the vertical protection already loaded in. In the rare exception case, it's easier to edit GRIFY->CELAK than to re-add AGANE. On the 34 side, expect vectors onto final and the occasional slam-dunk if a hole opens up.
GLASR
Named after Glacier Peak (do yourself a favor and avoid calling it “Glazzer”), you can expect vectors right after JAKSN toward the 16s, typically heading 230 or 240 down to 8000 or 7000, then down to 5000 to join. If it's busy, they may give you more of a dogleg like heading 270, then direct AGANE later, so don't be too eager to activate vectors-to-final. If approach wants you fast, go down first (FLCH) and be prepared to slow to 210 as you get close to AGANE. If it’s cloudy, expect icing in the descent as the clouds pile up on the western side of the Cascades. In the E175, plan to get normal and SPIS landing numbers. On the 34s, they sometimes leave you high or give you speed 210 further out on the downwind because they need the spacing. It’s often a good idea to grab some drag when they give you this to prevent ending up high. Again, watching the extended TCAS will help you plan.
CHINS
Similar to the GLASR, this one comes over the Cascades, but from the southeast. Prior to descent, check the winds aloft. If they’re 180-230 and >25 knots, you’ll be in the lee of Mt. Rainier and you should expect bumps in the descent. Help keep your teammates and passengers safe by giving them a heads up and seating them before that. Going to the 16s you can plan to descend at 250 to 5000, then 210 in the base. Going 34s, expect to get vectored 270 or 260 and dropped down to 8000 or 5000 a bit early. One threat to plan for when it’s nice out is GA traffic east of the Bravo shelf. If you see a bunch of targets on your TCAS, monitor 122.75 and listen for “Southeast Practice Area” calls. Every so often someone busts the Bravo, so don’t assume that you’re clear of GA there.
HAWKZ
Named after the Seattle Seahawks football team, the HAWKZ comes in from the southwest. Most of the Oregon and California traffic comes in this way, so expect it to be busy. Seattle Center will sometimes give you the “Seattle Shuffle,” where they vector you off course for a minute or two and then give you direct a downrange fix and a speed assignment. Coordination with Oakland Center is not always great: you might get .73 for spacing at first, then across the sector boundary you get a shuffle followed by .79 for spacing. I wish Oakland would just tell us “Cross BTG at time TTTT then maintain .MM” so we can punch it in the box and avoid the fuel-wasting silliness. If you get “Direct KNGDM,” be aware that the fix is named after the Kingdome where the Hawks used to play, not a monarchical country (“King DOME” not “kingdom”). On 34s, they usually join you from SONDR. On the 16s, check your winds aloft and plan your descent gradient accordingly. Especially in the winter you can get strong tailwinds between HAWKZ and PIKEZ, which with the slowdown might get tricky. Watch for traffic below you outbound on the HAROB and BANGR as you come through BREVE and NETTZ. As you come up on VASHN, you might get 3000 (slam dunk through Elliott Bay), 4000 (moderate descent to join at CELAK), or 5000 (mosey down to the end of the conga line). Listen for heavies if you get 16R, sometimes they get vectored below you to 16L (see drawing). You may see a TCAS target a bit below you that seems close, so listen for the names of fixes to that runway in their approach clearance and pipe up if you’re not sure where they’re going.
16R
16R is on a plateau created by fill. If you have a strong southerly or southeasterly, expect a sinker between 100-200 AFE as the air drops off the edge. If it’s a southwesterly (e.g. cold front), expect puffs, then a sinker followed by a floater as the air gets deflected up over the western edge of the plateau. One threat in the winter, when the sun is low in the sky after some drizzle, is that all north/south surfaces look shiny with the glare and it gets hard to distinguish them. A number of crews have landed on taxiway Tango. A good mitigation plan is to use an ILS or RNAV as backup and monitor the needle if you get a visual to prevent a wrong-surface event.
Named after the Seattle Seahawks football team, the HAWKZ comes in from the southwest. Most of the Oregon and California traffic comes in this way, so expect it to be busy. Seattle Center will sometimes give you the “Seattle Shuffle,” where they vector you off course for a minute or two and then give you direct a downrange fix and a speed assignment. Coordination with Oakland Center is not always great: you might get .73 for spacing at first, then across the sector boundary you get a shuffle followed by .79 for spacing. I wish Oakland would just tell us “Cross BTG at time TTTT then maintain .MM” so we can punch it in the box and avoid the fuel-wasting silliness. If you get “Direct KNGDM,” be aware that the fix is named after the Kingdome where the Hawks used to play, not a monarchical country (“King DOME” not “kingdom”). On 34s, they usually join you from SONDR. On the 16s, check your winds aloft and plan your descent gradient accordingly. Especially in the winter you can get strong tailwinds between HAWKZ and PIKEZ, which with the slowdown might get tricky. Watch for traffic below you outbound on the HAROB and BANGR as you come through BREVE and NETTZ. As you come up on VASHN, you might get 3000 (slam dunk through Elliott Bay), 4000 (moderate descent to join at CELAK), or 5000 (mosey down to the end of the conga line). Listen for heavies if you get 16R, sometimes they get vectored below you to 16L (see drawing). You may see a TCAS target a bit below you that seems close, so listen for the names of fixes to that runway in their approach clearance and pipe up if you’re not sure where they’re going.
16R
16R is on a plateau created by fill. If you have a strong southerly or southeasterly, expect a sinker between 100-200 AFE as the air drops off the edge. If it’s a southwesterly (e.g. cold front), expect puffs, then a sinker followed by a floater as the air gets deflected up over the western edge of the plateau. One threat in the winter, when the sun is low in the sky after some drizzle, is that all north/south surfaces look shiny with the glare and it gets hard to distinguish them. A number of crews have landed on taxiway Tango. A good mitigation plan is to use an ILS or RNAV as backup and monitor the needle if you get a visual to prevent a wrong-surface event.
34L
Usually, the winds are calmer on 34 days, but they might get squirrelly if there’s an inversion. If you see a stratus layer or low haze, watch for a wind shift. One clue is to look left at the ripples in the sound by Des Moines: if the water near the shore is glassy, there’s an easterly. If it looks darker near Des Moines (closer to the runway) and glassy near Vashon Island on the western edge of the channel, it’s a westerly.
Usually, the winds are calmer on 34 days, but they might get squirrelly if there’s an inversion. If you see a stratus layer or low haze, watch for a wind shift. One clue is to look left at the ripples in the sound by Des Moines: if the water near the shore is glassy, there’s an easterly. If it looks darker near Des Moines (closer to the runway) and glassy near Vashon Island on the western edge of the channel, it’s a westerly.
departures
Most of the departures are pretty straightforward. The MONTN flows out underneath the CHINS or GLASR (depending on north or south flow), and the HAROB and BANGR will take you under the HAWKZ or MARNR to the west. A lot of the time, your clearance will be up to 7000 (south flow) or 9000 (north flow). If departure tells you to stick with the assigned number, expect traffic above you on the corresponding STAR. I like to use the expanded TCAS to see them earlier and shallow the climb if it will be close to reduce TA/RA events, especially on the HAROB with overflying HAWKZ traffic. If you depart north, tower might tell you to stay with them for a while because there’s traffic in or out of KBFI just to the north. Watch for them. 32L at KBFI gets a lot of TA/RA events from GA traffic in the southeast practice area, so if they go around, they’ll be closer to your departure path.
Ground ops
180 on Tango
Sea-Tac is reportedly one of the busiest airports when viewed in terms of passengers moved per unit airport area. The ramps can get crowded during peak times. From north to south, there are a few access points: 55, 66, 77, 88, and 99. On the west side of the C/Q and B gates, there’s also taxilane W that’s ramp-controlled. One word of caution with the Q gates: their labeling doesn’t correspond to the gate number inside the terminal.
Ramp will often try to push a bunch of nearby planes together to clear the alley, then let arrivals in. Often, they will coordinate with tower and ground try to stage them on the taxiways before crossing 16L/34R in a big platoon and then send them into the ramp in sequence. Often, they try to time it when there’s a gap in departures behind a heavy and they need some time for wake dissipation. Otherwise they just build a hole every 5-10 outbounds, depending on how busy it is. Gauging where in this cycle you are can often help. If your gate is occupied, expect to be held on Tango between the runways away from the ramps. You may get a weird taxi instruction like “Airline 123 exit 16L on November, then left Tango, make a 180, and hold short November.” If you’re not expecting that, it can take a second to process what they’re asking you to do.
Ramp will often try to push a bunch of nearby planes together to clear the alley, then let arrivals in. Often, they will coordinate with tower and ground try to stage them on the taxiways before crossing 16L/34R in a big platoon and then send them into the ramp in sequence. Often, they try to time it when there’s a gap in departures behind a heavy and they need some time for wake dissipation. Otherwise they just build a hole every 5-10 outbounds, depending on how busy it is. Gauging where in this cycle you are can often help. If your gate is occupied, expect to be held on Tango between the runways away from the ramps. You may get a weird taxi instruction like “Airline 123 exit 16L on November, then left Tango, make a 180, and hold short November.” If you’re not expecting that, it can take a second to process what they’re asking you to do.
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South Flow
In south flow, the South Satellite traffic usually goes counterclockwise from 99 around to 88, while the North Satellite goes clockwise from 55 to 66. This will often dictate your taxi assignment from the runway. If you’re going to A or S, expect to get crossed at P or Q then 99 round to park. East side B gates you often get 99 as well, but if you see a bunch of people pushing off A4-A14 or S1-S6 before you cross 16L or leave B, you might be able to ask ramp if you can sneak in 88 against the normal flow while the alley is blocked. North Satellite into N, C, and D is similar. West side C and B is pretty straightforward, though ramp does want you to call them when ready to taxi instead of just going right over to ground. Tower, ramp, and ground are usually pretty good about coordinating inbound gate assignments, though they sometimes get it wrong if there are late changes. If you get an assignment that doesn’t match what you think your gate should be (e.g. “99 to park” when you’re showing B5), call ops before you stick your nose in an alley and clarify it with tower/ground/ramp as appropriate to save everyone some time and heartache getting you back out of that hole. Taxiing out, you may get a hold short if they’re crossing a platoon of inbounds, so watch for that. At rush hour (0730-0830 and 2300) it’s a good idea to go out single-engine if the line is long (I’ve been #23) and start the second one around Golf or Yankee. If they tell you to taxi up Alpha, you’re probably getting flow, common for destinations like Vancouver and San Francisco. Plan numbers for both 16L and 16C and expect a late runway change, so try to get everything as dialed in as you can. Sometimes they’ll switch you late to accommodate a heavy on 16L. I like to monitor tower and ground on the way up B so that either one can get a hold of us for either flow delays (usually ground asking you to pull onto A) or runway changes (usually tower). I’ve heard a few “Bueller” calls for crews that are on the other frequency, so it helps to have an ear on both. North Flow North flow is basically the opposite: clockwise 88 to 99 on the South Satellite, though North usually remains counterclockwise. After clearing 34L, expect to get crossed and south Bravo, or south Tango to cross closer to 88. |
South flow normal setup
Sometimes you can sneak in 88
North flow setup
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conclusions
As far as busy Class Bravo airports go, Sea-Tac isn’t too crazy. Your big threats and curveballs are:
- Nearby traffic for KBFI and GA on nice days.
- Slam-dunk visuals if there’s a hole to fill. Monitor the conga line and listen for the magical “descend and maintain 3000” to be prepared for this.
- Weather over the Cascades: check your winds on the CHINS and GLASR and be alert for ice, especially in the winter.
- Crosswind days during cold and warm fronts: plan an alternate that won’t leave you stranded if you need to get out of there.
- Crowded ramps and gate changes: listen for anything weird and double-click on anything that seems off. It could save you 15+ minutes of wasted taxi time if you get stuck around a satellite.
- Late runway changes: have plan B on speed dial so you can be ready in <2 minutes.