For the majority of passengers, the flight's cruising phase is a tranquil and calm time.
After the food service is finished, it's a good idea to relax and watch a movie, perhaps have another drink, or take a sleep.
If you're seated in business or first class, your seat has likely been reclined, and your bedding has likely been set up.
It can be simple to forget that you're actually in a pressurized metal tube flying through the air at 600 mph, 7 miles above the ground, when you're safe and cosy in your own little cocoon.
The environment at the front of the aircraft is very different from your sleep-inducing gentle bumps.
Your pilots are wide awake here, guiding the aircraft through the night sky while they are illuminated by the instrument panels.
They are fully aware of the aircraft's height, speed, and, most crucially, the terrain for the following few hundred kilometers.
At 39,000 feet, the tensions and strains of daily life can seem a million miles away.
However, it is these events—particularly the geopolitical ones—that have a significant impact on how flights work and the routes we take.
Where aircraft fly and don't fly
How many aircraft are in the air at any given time can be determined by taking a quick peek at Flightradar24.com.
The places without any planes are, nevertheless, of greater interest.
Airlines constantly keep an eye on the security situation in the nations that their aircraft are flying over, despite the fact that their aircraft are thousands of feet above the earth.
Some nations may not even be offering an air traffic service to allow planes to pass over their airspace, depending on the geopolitical situation.
An important corridor connecting much of North America and Europe with the Indian subcontinent, Eastern Asia, and Australia. Which concentrates on the Middle East and Western Asia.
There will be a requirement for this corridor to be used by almost all aircraft flying between these locations.
The Ukraine, Libya, Afghanistan, Nepal, and southwestern China, among other notable regions, display a dearth of planes going over them.
Other nations like Iran, Iraq, and Russia have much fewer flights than other regions, despite the fact that we do see some flights from those nations.
This is taken into account when airlines evaluate various routes and the likelihood of an aircraft mechanical issue necessitating a detour and landing.
There have been some bottlenecks created as a result of these route limitations, especially on the route via Egypt and Saudi Arabia.
Air traffic control delays, often known as "slots," are frequently the result of this. These slots limit the number of planes that can safely pass through a certain airspace at any one moment.
In order to avoid these congestion points and the ensuing delays while still maintaining passenger safety, airlines have begun looking at alternative routes for their aircraft.
One of the most intriguing of them is the flight path that passes via Turkmenistan, Uzbekistan, Tajikistan, Pakistan, and India.
Flying along the eastern border in Tajikistan and Pakistani airspace keeps aircraft purposefully out of Afghan airspace.
The "moving map" channel will display this specific itinerary for those passengers who are still awake.
The Himalayan mountain range is growing closer, which is another aspect of this path that the more perceptive may observe.
The coming mountains are very much on the pilots' minds as they sit in the serene silence of the flight deck.
Safe Minimum Altitudes
The aircraft's altitude is expressed in reference to mean sea level.
In other words, if a plane is flying over the ocean at 39,000 feet, then there is roughly 39,000 feet of air between the plane and the water (I say "pretty much" because there are different tolerances for air pressure changes when the aircraft moves from one place to another).
The distance between the aircraft and the nearest rock can be greatly reduced when flying over mountainous terrain.
For instance, if a mountain is 9,000 feet high (conveniently measured from mean sea level), even though the plane is at 39,000 feet, there would only be 30,000 feet between the aircraft and the hill.
Because of this, it's crucial for pilots to understand the lowest altitude at which they may fly in a specific location without colliding with any terrain.
The MSA, or minimum safe altitude, denotes this.
If the pilots must descend for any reason, this comes into play.
The MSA will consider any poles or masts situated on the top in addition to the mountain's height.
It would be catastrophic if the crew missed the rock and instead collided with the 500-foot telecom mast perched atop the hill.
Pilots are always mindful of the local MSA as they fly around the world.
This is typically 2,000 feet above the oceans to account for any huge ships or ships having scientific balloons above them.
On land, the MSA is much more of a problem and changes with the landscape organically.
The MSAs can ramp up quickly when flying over mountain ranges.
These MSAs can be so high that they present significant logistical issues for pilots when flying over the Himalayas, which is the highest and largest mountain range in the world.
On their tablet computers, the pilots have access.
The route around Afghan airspace is clearly displayed, as well as the MSAs for that route, which are shown without the last two zeros.
The lowest safe altitude to which pilots can descend is 19,800 feet because the MSA through southern Tajikistan and Uzbekistan is 198.
However, the MSA climbs to 28,700 feet as the aircraft round the bend and head south.
When do MSAs become effective?
A casual observer might not think that these statistics are an issue.
Considering that and plane is flying at 39,000 feet, even the highest MSAs are much above that altitude.
Thoughts about the future and "what if" scenarios are also important for a pilot to contemplate; they should not just focus on the present.
What if, in this case, a mechanical issue with the aircraft necessitated a descent to a lower altitude?
Those high MSAs are now a very important factor.
Consequently, what might demand that the pilots descend?
Your first thought likely revolved around the possibility of a cabin losing pressurization.
Decompression
An aircraft's cabin is pressurized so that you can breathe as though you are on the ground (or relatively close to it) even though you are traveling at a height of several miles.
This indicates that the air pressure within the cabin is greater than the air pressure outside the plane.
Most commercial planes have a "cabin altitude" of about 7,000 feet when they are flying at 39,000 feet.
The loss of cabin pressurization, commonly referred to as decompression, causes the cabin altitude to either gradually approach or quickly approach the actual altitude of the aircraft.
If this were to occur while the aircraft was in flight, the cabin's height would rise to a point where everyone within would be unable to obtain enough oxygen into their bodies and risk becoming hypoxic.
This is why oxygen masks descend during a decompression to allow everyone to breathe normally.
After everyone has put on their masks, it is the responsibility of the pilots to lower the aircraft to a level where mask use is no longer necessary.
Typically, this is at altitudes of 10,000 to 14,000 feet.
We do, however, have a dilemma on this path that we are taking to Asia.
The MSA is 28,700 feet, but the pilots wish to descend to 10,000 feet.
Clearly, the two are incompatible.
Engine failure
An engine failure is the other situation in which a descent might be necessary.
The lift a wing can provide at its current weight, the air's temperature, and the power of the engines are a few of the variables that affect an airliner's cruising altitude.
The flight management system will determine the best altitude when you include the wind information and the length of the route.
On the other hand, in the event that one of the engines must be shut down for whatever reason, the power that is now available will be decreased by 25% for a four-engine aircraft or by 50% for a two-engine aircraft.
Since all planes are built to fly safely in this situation, this situation by itself does not pose a safety concern.
As a result, the pilots may need to drop to a lower altitude where the aircraft can continue to fly safely with the remaining engine power. This could imply that the aircraft is no longer able to maintain its present altitude.
The aircraft's weight determines what is referred to as the drift-down height.
In order to maintain forward motion, a plane must have greater engine power as its weight increases since heavier aircraft require more wing lift to fly.
A decreased drift-down altitude will happen as a result.
The drift-down altitude, however, will rise as fuel is burned and the plane gets lighter.
The issue arises on lengthy flights, like the one from Amsterdam to Singapore, where an aeroplane like the 787's drift-down altitude is possibly 23,000 feet, which is much lower than the MSA of 28,700 feet.
So what should pilots do if there is a decompression or engine shutdown over a region with such a high MSA?
The solution is a way out.
Escape routes
The flight operations division of the airline will assess the worst case scenario, which is a mandatory descent to an altitude much below the highest MSA at any time, for any route with significant MSAs like this.
Then they will design an escape path that enables the pilots to steer clear of the mountainous terrain before descending to 10,000 feet in the event of a decompression or to the drift-down altitude in the event of an engine failure.
Since a plane like the 787 can keep everyone on board with oxygen for around two hours, the decompression scenario is actually the least problematic.
In this scenario, the pilots will descend to the MSA of 28,700 feet and begin to turn away from the steep terrain as directed by the escape route.
This strategy will also let the crew know when it is safe to drop to a lower altitude.
As a result, if you were in an aeroplane that had a decompression over high ground, you might not have noticed much descent for a long.
This is due to the pilots' deliberate decision to wait until they are above the mountains before descending to a lower altitude.
The aircraft can only maintain its present altitude for a limited period of time, making the engine failure situation more serious.
When an engine is turned off, the airspeed decreases to the point that the plane begins to slowly descend to the drift-down altitude, hence the name.
It is therefore essential that the pilots begin directing the aircraft into the escape path and toward the lower terrain before it flies below the MSA, which is a condition we never want to be in.
We can unwind a bit more and consider the next phase of the flight: a detour to a nearby airfield, after we are out of the high terrain and over an area where the MSA is lower than 10,000 feet (in the case of decompression) or our drift-down altitude (in the case of an engine shutdown).
In conclusion
Airlines must research new routes in order to get people to their destinations as quickly as feasible given the current state of the planet.
Pilots must constantly be mindful of their location in respect to mountains since some of these routes take planes over hostile terrain.
We always prepare for the worst case scenario because safety is our top priority.
As a result, in the unusual event that it does, we are ready, have a plan in place, and are aware of exactly how to handle the situation to keep our passengers safe.
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