The journey period of a flight is a time of relaxation and serenity for most passengers. When the food service is over, it’s a good time to sit back and watch a movie, maybe have another drink or take a nap. If you’re sitting in business or first class, you may have reclined your seats and arranged your bed.
Safe and comfortable in your own little cocoon, it can be easy to forget that you’re actually inside a pressurized metal tube cruising through the air at 600 mph, 7 miles above the ground. When a slight collision puts you to sleep, the scene in front of the plane couldn’t be more different.
Here, surrounded by instrument panel lights, your pilots are awake navigating the plane through the night sky. They know the exact altitude of the plane, its cruising speed, and most importantly, what lies ahead for the next few hundred miles.
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At 39,000 feet, the pressures and stresses of life on the ground seem millions of miles away. However, it is these events, especially geopolitical ones, that play an important role in how a flight works and the routes we fly.
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Where do planes fly and don’t fly
A quick look at Flightradar24 will show how many planes are flying around the world at any given time. However, what is of most concern are the areas where there are no planes.
Even though planes are flying thousands of feet above the ground, airlines are always monitoring the security situation in the countries where their planes are flying.
Indeed, depending on the geopolitical climate, some countries may not even provide air traffic services to allow planes to fly through their airspace.
The image above focuses on the Middle East and West Asia – a major corridor connecting much of North America and Europe with the Indian subcontinent, East Asia and Australia. Almost all aircraft traveling between these areas will need to fly through this corridor.
However, some notable areas on the map show a lack of flights over them, such as Ukraine, Libya, Afghanistan, Nepal and southwestern China. Also, there are other countries that, although we see some flights, are much more limited than others, such as Russia, Iraq and Iran.
This number gives an assessment that airlines make about certain routes and what happens if one of their planes experiences a technical problem that forces them to divert and land.
Due to these route limitations, certain bottlenecks have developed, especially on the route through Egypt and Saudi Arabia. This often leads to air traffic control delays, or “blanks,” which ensure that only a certain number of aircraft fly through that airspace in a given time, a number of planes. which ATC can safely handle.
As a result, airlines have been exploiting other routes their planes may take to avoid these bottlenecks and inevitable delays, while ensuring the safety of all passengers. people on the plane. One of the most interesting of these is the route through Turkmenistan, Uzbekistan, Tajikistan, Pakistan and to India.
Related: How to track where your plane is coming from before your flight
The route deliberately kept the planes out of Afghan airspace, sending them along the eastern border over Tajikistani and Pakistani airspace. Passengers who remain awake and watch the “travel map” channel will notice this exact route.
The more observant may also notice another feature of this route: The Himalayas are getting closer and closer.
In the stillness of the flight deck, the approaching mountains loomed large in the minds of the pilots.
Minimum safe altitude
The altitude at which the aircraft is flying is relative to mean sea level. So when flying over the ocean, if the plane is at 39,000 feet, there’s pretty much 39,000 feet of air between the plane and the water (I say “pretty much” because there are different tolerances for variation). changes in air pressure as the plane moves from one area to another).
When flying over mountainous terrain, the distance between the aircraft and the nearest piece of rock can be significantly reduced. For example, if a mountain is 9,000 feet high (which can also be conveniently measured from mean sea level), even if the plane is at 39,000 feet there is only 30,000 feet between the plane and the hill.
It is therefore essential that pilots know the lowest altitude at which they can fly in a particular area while remaining clear of the terrain. This is called the minimum safe altitude, or MSA. This comes into effect if the pilots need to descend for any reason.
The MSA will not only take into account the height of the mountain, but also any poles or masts located on top of the mountain. It would be tragic if the crew slipped and crashed into a 500-foot telecommunications mast located at the top of the hill.
As pilots fly around the world, they always know about the MSA in their area. Over the oceans, this altitude is typically 2,000 feet, taking into account any large ships or ships with science balloons above them. On land, the MSA is more problematic and varies naturally with the terrain.
Related: How do pilots decide how high they fly?
When flying over mountain ranges, the MSA can accelerate rapidly. When flying over the highest and largest mountain range in the world, the Himalayas, these MSAs can be so high that they can pose serious logistical challenges for pilots.
The image below is the chart that the pilots have available to them on their tablet devices. It clearly shows the route around Afghanistan airspace, and especially the MSA for that route, shown with the last two zeros removed.
So over southern Tajikistan and Uzbekistan, the MSA is 198, which means the lowest safe altitude a pilot can descend is 19,800 feet.
However, as the plane turned the corner and flew south, the MSA rose to 28,700 feet.
When does the MSA go into effect?
These numbers are unlikely to be a problem to the casual observer. After all, if an airplane is flying at 39,000 feet, that’s even higher than the MSA peak. However, the role of a pilot is not only thinking about the here and now, but also about what’s to come and consider the “what if” scenario.
In this case, what if the plane had a technical problem that caused it to descend to a lower altitude? Suddenly, those high MSAs were a very real consideration. So what might require the pilots to descend?
The first scenario that might come to your mind is depressurization of the cabin.
To reduce pressure
To allow you to breathe as if you were on the ground (or near it) despite flying several miles above the earth’s surface, the cabin of the plane is pressurized. This means that the air pressure inside the cabin is higher than the pressure in the atmosphere outside the aircraft. The “cabin altitude” for most aircraft is about 7,000 feet when the plane is flying at 39,000 feet.
The loss of cabin pressure, also known as depressurization, results in a slow or rapid cabin altitude equal to the actual altitude of the aircraft. If this happens in flight, it means the cabin altitude will become so high that passengers cannot get enough oxygen into their systems and may become hypoxic.
This is why, in the event of decompression, the oxygen mask will drop down so that everyone can breathe normally.
Once everyone is wearing masks, it is the pilot’s job to lower the plane to a high altitude without the need for masks. This is typically between 10,000 and 14,000 feet.
However, on the way we were flying to Asia, we had a problem. The pilots wanted to descend to 10,000 feet but the MSA was 28,700 feet. The two are clearly incompatible.
Engine failure
Other times it may be necessary to decelerate in the event of an engine failure.
The altitude at which an aircraft flies is determined by a number of factors including the lift the wing can generate at its current weight, the air temperature, and the available power from the engine. Add detailed information about the wind and the length of the route ahead and the flight management system will generate the optimal altitude.
However, if one of the engines needs to be shut down for any reason, the available capacity is reduced by 25% on a four-engine aircraft or 50% on a twin-engine aircraft. This is not a safety issue in itself as all aircraft are designed to fly safely in this case.
However, it could mean that the plane can no longer maintain its current altitude, so pilots will have to descend to an altitude where the remaining engine power can keep the plane safe. whole. This is called the descent altitude and it depends on the weight of the aircraft.
The heavier the plane, the more lift it takes from the wings to fly, so more engine power is needed to keep it moving forward. As a result, the drift altitude will be lower. However, as the aircraft burns fuel and becomes lighter, the descent altitude will increase.
Related: How airplanes are designed to operate when engines fail
The problem occurs on a long flight, for example between Amsterdam and Singapore, where the drop altitude of an aircraft like the 787 can be 23,000 feet, significantly lower than the MSA’s 28,700 feet.
So in the event of decompression or engine shutdown in such high MSA areas, what are pilots supposed to do? The answer is a way out.
Escape routes
For any route with a significant MSA like this, the airline’s flight operations department will assess the worst possible scenario, namely a necessary descent to an altitude lower than the MSA. highest at any given time. They would then create an escape route that would allow the pilot to navigate off high terrain before descending to 10,000 feet in the case of depressurization or to descending altitude in the event of an engine shutdown.
The decompression case is actually the least relevant since planes like the 787 can supply oxygen to all on board for about two hours. In this case, the pilots would descend to the MSA at 28,700 feet and begin to turn away from the high terrain, as specified by the exit route.
The plan will also notify the crew of when it may be safe to descend to a lower altitude. Therefore, if you’re on an aircraft that has experienced a depressurization over high terrain, you may not notice much of a drop going on for quite some time. This is because the pilots are making sure they are clear of the mountains before descending to a lower altitude.
Engine failure is even more serious because the plane will only be able to maintain its current altitude for so long. With the engine off, the airspeed will decrease to such an extent that the aircraft will begin to decelerate (hence the name) to the deceleration altitude.
As a result, it was imperative for the pilots to guide the aircraft onto the exit route and to lower ground before the plane went lower than the MSA – a situation we never wanted to encounter.
Once we had left the high ground and passed an area with an MSA lower than 10,000 feet (in the case of depressurization) or our deceleration altitude (in the case of engine shutdown), we could relax for more than a minute. Take a moment and think about the next stage of the flight: redirect to a nearby airport.
Key point
With all that is going on in the world, airlines have to explore new routes to get passengers to their destinations as efficiently as possible. However, because some of these routes take planes over harsh terrain, pilots must always be aware of their position in relation to the mountains.
Since safety is our #1 priority, we always plan for the worst case scenario. So in the unlikely event of an accident, we are prepared and know exactly how to respond to an incident and keep our passengers safe.
