Opinion: What does this pilot know about flying in mountainous terrain

Editor’s Note: Les Abend was a Boeing 777 captain for American Airlines, retiring after 34 years with the airline. He is a CNN aviation analyst and a senior contributor to Flying magazine. The opinions expressed in this commentary are their own. see more opinion on CNN.


Circumstances leading up to Nepal’s deadliest plane crash in 30 years is still in the early stages of the investigation. But that hasn’t stopped the media’s focus on the mountainous terrain and the unique challenges it poses for pilots.

Les Abend

Nearly all of the bodies of the 72 people on board, including the crew, have now been found after a Yeti Airlines ATR-72 plane crashed Sunday while approaching the newly opened airport. in Pokhara, a tourist destination and gateway to the Himalayas.

Assuming the accuracy of mobile video Taken just before impact, it appears that the plane began to tilt its wings at a too steep angle. In addition, the yard attitude – the angle of the nose relative to the horizon – seems unusually high.

In this pilot’s opinion, the plane had entered an aerodynamic stall, meaning the wings were no longer capable of providing lift for sustained flight. A near-ground recovery is virtually impossible. What caused the stall? It will remain a mystery until more details of the investigation are revealed. Weather doesn’t seem to be a factor.

Much has been said about dangerous to fly over the Himalayas, but it is no more challenging than any other geographical area in the world with high terrain. Regardless, the strategy is to minimize risk. But how?

Having flowed into and over areas that share space with the Andes in South America, the Swiss and French Alps, and the Rocky Mountains of the United States, I see knowledge as a form of risk reduction. best ro. In the flying business, we call this knowledge situational awareness.

Where is the elevation relative to the aircraft’s current position and its future position? What is the terrain threat during takeoff or landing? If an engine fails on takeoff, what procedure can we follow to return safely to the departure airport? And on approach, at what altitude is it safe to decide whether to abort or continue?

My airline has specific procedures in place in the event of an emergency diversion over high altitude at cruising altitude. They involve specific exits with precise minimum altitudes that allow our flight to continue safely to an alternative destination.

Because some airports in the Himalayas have terrain so high that aircraft cannot pass on initial departure, landings are conducted from one direction, with takeoffs in the opposite direction.

This can become a problem if a strong enough headwind exists. (Aircraft performance at takeoff is improved in crosswinds and reduced in crosswinds. Landing headwinds pose a risk of high ground speeds potentially sending the aircraft farther down the runway upon landing.) and may deviate from the endpoint.) That’s why an airline imposes wind limit for airports and airplanes.

Rescuers gather at the scene of a plane crash in Pokhara on January 15, 2023.

Higher altitude reduces aircraft and engine performance. Less dense air is not as conducive to wing lift as air at sea level. Less dense air reduces engine performance. Lower efficiency translates into a need to reduce aircraft weight through passenger and/or cargo loads because more runways are needed for take-off. But these factors are minimized through the use of graphs and performance charts, with computer calculations performing most of these tasks.

Another aspect of risk reduction is understanding the weather caused by mountainous terrain, commonly known as terrain lifting, which may be unique to each region. Depending on the direction of the wind, lifting the terrain can create turbulence, making cruising uncomfortable but difficult to approach.

Turbulence can require constant pilot attention and skill set to maintain a steady flight path, especially for aircraft not operating on autopilot. Good judgment and proper preparation are the best defenses.

Lower cloud ceilings and lower visibility pose challenges in high terrain because pilots cannot see the mountains to avoid the threat. The flight crew must rely on procedures relating to a instrumental approachThat’s what we train and practice to do.

The instrument approach process uses guidance from our in-flight navigation and main flight screens, without the need for visual reference to the outside world. And some airports only require visual contact with the runway at all times without an instrument approach procedure in place.

Many high-altitude equipment access procedures use ladder heights to maintain the required altitude above ground level. The allowed altitude becomes lower as the aircraft approaches the runway. The aircraft reached a point in the approach where it reached the “decision altitude”.

Decisive altitude is the point at which if the crew does not make visual contact with the runway, they must detour and abandon the approach. One go round is a procedure that both air traffic control and pilots are familiar with. This procedure always involves climbing and routing to a specific navigable point where the aircraft can enter the hold pattern.

Contingencies for procedures are always considered. For example, how does the procedure change for an engine failure, which reduces the aircraft’s ability to fly over high terrain? The best risk reduction is simple. It is the captain’s privilege and responsibility not to depart in bad weather.

High-altitude operations can be challenging for pilots. But the danger lies not in the terrain itself, but in how to reduce this risk. The Himalayas are no different.


News 7D: Update the world's latest breaking news online of the day, breaking news, politics, society today, international mainstream news .Updated news 24/7: Entertainment, the World everyday world. Hot news, images, video clips that are updated quickly and reliably

Related Articles

Back to top button