The pilot's view on the London Heathrow final approach

Of all the airport approaches around the world, the view landing into London Heathrow over London is hard to beat. Get yourself a seat on the right-hand side of the aircraft and you'll be treated to a bird's-eye view of the Tower of London, Buckingham Palace and the London Eye, to name just a few sights.

Last week I described the early stages of the approach, from leaving the cruising altitude down to turning toward the runway. So how do we fly the aircraft the last few miles to touchdown and just how complicated is it? This is the second part of a two-part series.

Runway alternation

London Heathrow has two parallel runways facing east/west. As aircraft landing and takeoff performance are optimized when flying into the wind, aircraft make their approach in over central London when the wind is coming from the west. In this direction, the runways are designated 27L (two-seven left) and 27R (two-seven right).

To keep things simple, Air Traffic Control uses one runway for takeoff and one runway for landing. So which runway do we use and when?

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Keeping the noise down

Located at the western end of London, Heathrow is acutely aware of its geographic position and the effects aircraft noise has on its neighbors. This noise comes from two sources: the sound generated by the aircraft's engines and also the sound created from airframe drag. The first is self-explanatory, but what is airframe drag and how does it create noise?

If you've ever held a large stick or object in the fast-moving flow of a river, you'll have noticed two things. Firstly, the water downstream of the object becomes disrupted and turbulent. Secondly, this turbulent flow creates a rushing sound. This is known as parasitic drag and is exactly what causes the noise from aircraft.

When flying in the "clean'" configuration (with slats, flaps and landing gear retracted) the aircraft is as aerodynamic as it can be. This results in minimum drag. As soon as these surfaces move out into the airflow, the drag increases and more noise is generated.

Read more: How pilots avoid runway overruns https://youtu.be/F9EFx7aQuhw

Parasitic drag generating noise

The greatest culprit for this type of noise is the landing gear. When we are ready to deploy the landing gear, the gear doors open into the airflow. This immediately increases the drag and a noticeable increase in noise can be heard, even in the cabin. With the doors open, the landing gear can then extend, increasing the drag and noise even more. When the gear is down, depending on the aircraft type, some of the gear doors close again. Onboard the aircraft, a noticeable reduction in noise can be observed at this point.

The faster the aircraft is flying, the greater the parasitic drag and therefore the greater the noise generated.

The 3 p.m. change over

To reduce the effects of noise on local communities, the airport switches the runway usage at 3 p.m. every day. This means that, for example, the northern runway will be used for landings from when the airport opens at 6 a.m. until 3 p.m. At this point, aircraft will then be switched to land on the southern runway until the last flight of the day departs.

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This system continues for a week at which point the alternation is switched again. Aircraft will use the southern runway for landings in the morning and the northern runway in the afternoons.

This means that those living under the approach path for one runway will get respite from the noise in the mornings one week and in the afternoons the next.

'TEAM' arrivals

While the airport sticks to the runway alternation as much as possible, in certain situations both runways are used for landing. If there are significant delays for arriving aircraft of 20 minutes or more, ATC is permitted to use both runways for landing.

Tactically Enhanced Arrivals Mode (TEAM) is allowed after 7 a.m. on westerly operations and enables six aircraft to land on the designated departure runway per hour. In addition to this, dual landings are also used during the busiest time of the day for arrivals, between 6 a.m. and 7 a.m. where there is no limit to the number of aircraft that can use both runways.

What does this mean for pilots?

In terms of how we fly the approach, both runways are very similar. The runway in use for landing will be notified to us well in advance, normally back in the cruise. We must then ensure that we have programmed the Flight Management Computer to capture the ILS for the correct runway. This is particularly important when TEAM is in use and aircraft are landing on both runways.

Both approaches tend to be ILS approaches and both have a rapid exit taxiway roughly the same distance from the touchdown zone. This means that we are able to use the same brake setting to slow the aircraft enough to vacate the runway as expeditiously as possible. With the next aircraft close behind us, ATC does not appreciate us staying on the runway longer than necessary.

The main difference between the two approaches is the Missed Approach Altitude in the case of a go-round. When landing on 27R, the missed approach altitude is 3,000 feet. On 27L, it is 2,000 feet. A fairly obvious difference, but setting the wrong value when landing on 27L could result in a confliction with a departing aircraft should we end up having to go around.

Keeping safe separation

Once established on the ILS to the correct runway, the next thing we need to think about is maintaining the correct spacing from the aircraft ahead.

When aircraft fly, they create a phenomenon known as wake turbulence. As the wing cuts through the air, there is a decrease of pressure above the wing and an increase below the wing. As a result, at the tip of the wing, there is a difference of pressure, which wants to roll up and over the top of the wingtip. It's for this reason why some aircraft have winglets, to block this downward force and increase wing efficiency.

The other consequence of this rolling air is the creation of wake vortices. Forming tornado-like swirls out from the rear of the wingtip, the fast-moving air can pose a serious threat to aircraft behind. The heavier and slower the aircraft, the greater the vortices generated.

To keep the trailing aircraft safe from the vortices of the leading aircraft, ATC ensures that there is sufficient separation. The distance or time of this separation depends on the type of both the aircraft generating the wake and the aircraft following. For the most part, the greater in size the leading aircraft is than the following aircraft, the bigger the gap.

In years gone by, aircraft were separated by a physical distance. For example, there would be a four-mile gap for an A340 following a Boeing 767. For an A320 following that A340, the distance would be five miles. This rigid system became even more of a problem during strong winds. Even though the speed over the ground of the aircraft was much slower, the distance between them had to remain the same. This drastically reduced the number of aircraft which could land in an hour.

However, with further studies of wake vortices and how the wind affects them, a new method was developed -- RECAT-EU. Instead of using a fixed distance, the new system utilizes time to keep the aircraft safely separated. As a result, the distance between the aircraft can be safely reduced.

The A340 mentioned above could fly safely just 2.5 miles behind the 767 and the A320 could fly four miles behind the A340. Add all this extra space up and you have enough capacity to land more aircraft in a day. A 2018 study found that with this new system, Heathrow was able to land around 1.4 extra aircraft an hour, roughly 22 extra flights a day.

Speed control

In order to keep the required separation, ATC instructs us to fly a certain speed. When intercepting the ILS, we will normally have been told to fly at 180 knots (207 mph). We then fly this speed until we are as close to the aircraft in front as safely possible. The only person who know when this point occurs is the controller.

At this point, they instruct us to slow to 160 knots (184 mph). This is normally around nine miles from touchdown, or as we call it "9d." When flying an ILS, the distance to touchdown is given in "Distance Measuring Equipment" (DME or "d" for short) and is roughly the same as nautical miles.

We then maintain 160 knots until 4d and this is absolutely key. It is imperative that all pilots strictly adhere to these instructions otherwise the whole system will fall apart. Fly too fast and you'll catch up with the aircraft in front. Fly too slow and the aircraft behind will catch up with you. The entire system hinges on pilots accurately flying 160 knots to four miles. After this, we are then free to slow to our final approach speed. For a heavy 787, this may be 155 knots. For a light A319, it could be 120 knots. No matter how different the final approach speed, so long as pilots maintain "160 to 4," there will be enough time for the leading aircraft to vacate the runway before the following aircraft touches down.

https://youtu.be/oTfgYbr82bc?t=417

How we fly it in a 787 Dreamliner

Flying down the ILS at 180 knots, we will normally have Flap 5 set with the gear up. With around 12 miles to run, we will be descending through 4,000 feet. On the right of the aircraft are stunning views of central London. The Houses of Parliament and Buckingham Palace slide past the window as we head toward Fulham. The "Stadium Tour" continues as we pass Stamford Bridge, home of Chelsea FC and the Craven Cottage, home of Fulham FC.

It's at around this point that ATC instructs us to slow to 160 knots. Depending on the weight of the aircraft, more flap is required to fly this slower speed, usually Flap 20. We then have 20 seconds to lose excess speed. As the Dreamliner is so aerodynamically efficient, it doesn't like slowing down. As a result, we have to use the speed brake, the large panels on top of the wing, to slow the aircraft down.

At this point, ATC will hand us over to the controllers in Heathrow Tower.

With the speed back at 160 knots, the River Thames bends away to the north up toward Hammersmith Bridge before coming back down to meet us. Some of you will recognize this section of the river as the course of the Boat Race -- the annual dual between the Universities of Cambridge and Oxford.

The next event on the flight path is to lower the landing gear. As mentioned above, the landing gear is one of the main generators of aircraft noise. As a result, we try to lower the gear as late but as safely as possible. For an aircraft the size of the 787, this is done around 2,000 feet above the ground, roughly 6d. Smaller aircraft, such as the A320 family, can leave this till later in the approach.

At 4.5d, passing Twickenham rugby stadium on the left, we take the final stage of flap, normally Flap 25 so that as soon as we hit 4d, we can reduce the speed to our final approach speed. Once again, if this is much slower than 160 knots, we will need to actively manage the speed by using the speed brake. We then complete the Landing Checklist.

Stable approach

With the gear down, landing flap set and flying the final approach speed, we reach our "make or break" point -- the 1,000 feet call.

At 1,000 feet above the ground, all the pilots in the flight deck must confirm that the aircraft has met certain parameters for landing. The aircraft must be at or close to its final approach speed, on the correct vertical profile and in the landing configuration -- landing flap set with the gear down.

If these criteria have been satisfied, the aircraft is declared as “stable.” If any of these have not been met, the aircraft is “unstable”‘ and a go-round must be flown.

From here, it's just a matter of minutes until touchdown. The pilot flying the aircraft will disconnect the autopilot and fly the last 1,000 feet by hand and land the aircraft manually.

Bottom line

Landing an aircraft at London Heathrow takes some serious concentration. With so many other aircraft around, it's imperative that pilots adhere to the instructions given to them by ATC. Even though the autopilot does the physical flying, it's the pilots who are instructing it what to do. On a clear day, the approach in over London is second to none. With some spectacular views to be enjoyed, I always opt for a window seat on the right-hand side when I'm a passenger. No matter how many times you fly this approach, you never tire of the views.