# Why is it more difficult for ATC to manage a larger airliner?

After playing a few ATC simulation games, and reading at a few places (don't remember where), I am certain that it is more difficult to manage a larger airliner for the ATC.

Suppose that one A320 and one A380 is trying to land at a certain airport. In another case, if two A320s are queuing up for landing, what extra precautions would the ATC have to take in first case, mainly in separating the aircraft and ensuring that they are on time?

They must leave a greater amount of time in between landings/take-offs as the size of the aircraft increases due to wake turbulance

There were historically 3 classes of aircraft for the purpose of wake turbulance classification

• H (Heavy) aircraft types of 136 000 kg (300 000 lb) or more;
• M (Medium) aircraft types less than 136 000 kg (300 000 lb) and more than 7 000 kg (15 500 lb); and
• L (Light) aircraft types of 7 000 kg (15 500 lb) or less.

With the introduction of the A380-800, where it is near MTOW, a fourth category has been added

• Super Heavy for Airbus A380-800 with a maximum take-off mass in the order of 560 000 kg

How much time must be left? Well that depends, for an A380:

Arriving Aircraft

• MEDIUM aircraft behind an A380-800 aircraft — 3 minutes;
• LIGHT aircraft behind an A380-800 aircraft — 4 minutes.

Departing Aircraft

3 minutes should be applied for a LIGHT or MEDIUM aircraft and 2 minutes for a non-A380-800 HEAVY aircraft taking off behind an A380-800 aircraft when the aircraft are using:

1. the same runway;
2. parallel runways separated by less than 760 m (2 500 ft);
3. crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1000 ft) below;
4. parallel runways separated by 760 m (2 500 ft) or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1 000 ft) below.

Source for timings: http://www.skybrary.aero/index.php/Airbus_A380_Wake_Vortex_Guidance

Multiple reasons I can think of (but I'm no pilot so I may be wrong!):

1. Bigger aircraft are more constrained in terms of which runways they can accept clearances to land on & take off from
2. Bigger aircraft typically need more room to maneuver into holding patterns, change Flight Levels, make turns etc.
3. Larger aircraft cause more wake turbulence and need to be provided larger separation behind them especially if the following aircraft is much smaller in size
4. Bigger aircraft need longer to slow down and are constrained in which taxiways they can exit via. or whether they will accept LAHSO clearances
5. Bigger aircraft (especially the really big ones) typically have fewer options in terms of parking bays, ramps, tugs etc. that can service them which imposes further restrictions for ramp controllers and ground movements.
6. Bigger aircraft have higher stall speeds in general and higher landing speeds too. So a controller is limited in how much (s)he can ask a Heavy to slow down while executing his plan.
• Would any size airliner accept a LAHSO clearance? For that matter, would any jet accept (or be offered) a LAHSO clearance? Also, larger airliners don't necessarily land much faster than smaller ones. Depending on how much weight it's burned off in flight, a 777 might actually land slower than a 737. Jul 23 '15 at 19:44
• @reirab -- they'd check their performance charts -- the LAHSO distances at some airports are longer than the full runway length at other jet-served airports (such as DCA or MDW). Jul 23 '15 at 23:05
• @reirab: Stall, and landing, speeds depend mostly on the design cruise speed of the aircraft, so since most jet airliners are designed to cruise at M0.85, they also land at similar speed. Turboprops are designed for lower speed and have correspondingly lower landing speed. Jul 24 '15 at 9:15
• @JanHudec Right, that was my point. Landing speed depends mostly on design cruise speed, weather, and current weight relative to MTOW, not so much the actual size of the aircraft. Small jets generally land at speeds very similar to those of heavies, contrary to the implication of point 6 above. Of course, turboprops (and especially pistons) will generally be slower, due to being designed for lower flight speeds. Jul 24 '15 at 13:35
• @reirab, I was just confirming it, yes. Jul 24 '15 at 13:39

I wouldn't say more difficult. But it definitely needs extra care. That's mostly for 2 reasons:

1. Inertia. Bigger aircraft have more mass, more inertia and thus cannot change their kinetic status easily. So ATCOs should have that in mind when vectoring aircraft and should issue commands earlier.
2. Wingtip vortices. Wingtip vortices are a function of lift. More lift is needed to keep a heavier aircraft flying, so this aircraft will cause more powerful wingtip vortices. Those can be dangerous and pose a threat for planes landing right behind heavier ones.