Airport Mexico City

Exceptional airports: Mexico City

Tim Takeoff
5 minutes

After we have already taken you on exciting flights to New York and Hong Kong, today the journey takes you to South America. More precisely to the capital of Mexico: Mexico City.

The international airport of Mexico City (ICAO code MMMX) was first expanded and used as a civil airport in 1928. It quickly developed into a central point of contact for all travellers to Mexico and a transshipment point for freight air traffic. In fact, it is so centrally located that during the day it hardly stands out from the chaotic cityscape, as it is right in the middle of the metropolis of millions.

Impressive figures

As if this were not special enough, let us look at the following facts from the perspective of an airman:

Even if one has only a limited aeronautical background knowledge, it should now be clear that these data do not necessarily correspond to the ideal conditions.

Thin air – and its effects

As a pilot you are already impressed by the pure density altitude. Moving a transport aircraft on a terrain more than 2,000 meters high causes many problems. The thin air causes the jet to need completely different speeds to generate sufficient lift. At this altitude you fly at a speed of about 20 to 40 knots higher than at sea level. This corresponds to about 40 to 75 km/h. It is because the aircraft’s measuring instruments measure the pressure of the air particles in the so-called “jam tube” or “pitot tube”.

Air particles

These are the same air particles that generate lift on the wing. Since there are simply fewer air particles at altitude, you are actually flying much faster than shown on the pilot’s displays. In addition, the speed above ground, and thus the required sink rate compared to the ground, increases drastically. A normal jet at sea level requires a sink rate of about 500 to 700 ft/min around the glideslope (more on this in our article on approach procedures), whereas the pilot in Mexico City has to allow for more than 1,000 ft/min.

This consequently means that, when landing, a particularly long distance is required to bring the jet to a standstill. Mexico’s runways have been extended over the years to accommodate the growing size of the jets. The current runway length of the longest runway “23 Links” is 3,825 meters.

A small, academic excursion into the speeds of aviation:

Indicated Airspeed, IAS

True Airspeed, TAS

Ground Speed, GS

A short example for comprehension: On approach to Mexico City at 5,000 feet above ground (i.e. 13,000 feet above sea level), a jet flies at a speed of about 220 knots according to IAS without the need for flaps (clean speed). Due to the thin air at this altitude, the TAS is then already 260 knots. Above ground (GS), with a typical tail wind of 20 knots, this is already 280 knots, i.e. over 500 km/h.

Mexico City – Flying in the highlands

But until one gets to the runway, one has to fly into a valley basin at a higher speed. In case of bad visibility or storm, pilots must follow the exact approach procedures. The mountains in the west rise up to 4,000 metres, in the east there are the active volcanoes Popocatepetl and Iztaccihuatl with over 5,000 metres of altitude. Both volcanoes regularly emit ash clouds, which must be closely monitored in order to assign the jets the appropriate approach route.

Such difficult weather conditions, in addition to the storms that occur, make it more likely that a diversionary landing at a distant airport will be necessary in Mexico if parameters change at short notice.

What if…?

Should problems occur during approach or take-off which limit the performance of the jet (such as engine failure), the pilot must follow procedures specially designed for the particular type of aircraft. The power would no longer be sufficient to get over the mountains in one “slip” with the full continuous power of the remaining engines. An aircraft is then usually flown into a kind of holding pattern via fixed routes (the so-called “Engine Out Standard Instrument Departure Route”). In this loop, the jet can then calmly climb to the necessary altitude to safely combat the problem or head for an alternate airport if a landing in Mexico City is not possible (due to weather or other reasons).

Training in the simulator

In order to meet all these requirements and also to be able to better convey the situation to new pilots, most airlines send their crews to the simulator before they visit a demanding airport (see article Flight Simulator). Here, numerous situations can be simulated without danger. High and low weights, engine failures during take-off and landing, the effects of high temperatures and storms, even volcanic eruptions can be conjured up on the screen by the trainer.

All these measures are necessary so that passengers can discover one of the most impressive countries in the world without any worries. Have you ever stood in the basket of a hot air balloon at sunrise over the Aztec pyramids? If not, be sure to plan a trip to Mexico!

by Tim Takeoff

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