dailynewsnblog
Roots In Early US/British Influence On Aviation
Why the foot is the standard unit used by pilots, and the meter is not, is actually a very simple question to answer: Feet were used by the Wright brothers. That is, altitude measurements were given in imperial values during the world’s very first flights, and the practice sort of just stuck.
After the duo achieved their first flight, aviation became heavily influenced by the United States and the United Kingdom. Why the Wright brothers had initially opted to express height through feet was purely down to the standard use of imperial units in the US. This, alongside the fact that imperial was the standard in the UK, meant that the foundations on which aviation was developed included units such as feet for measurement.
Perhaps such a practice might have been fairly simple to drop once upon a time, but today’s technology would make it far more complex. Aircraft instruments, charts, procedures, and air traffic control systems, to name a few, largely evolved from those early models developed in the UK and the US. In practice, that meant such hardware and methodology relating to altitude were calibrated in feet from the beginning and have remained that way since.
Move To Metric Was Actually Recommended By ICAO
It is not like no one has pushed for the metric system to take over in the aviation space. Over the years, several attempts have arisen, only to fall flat as tradition, or perhaps common sense, prevailed.
Back in the early 1970s, the International Civil Aviation Organization (ICAO) recommended that the industry transition to metric. Given ICAO’s position as a governing body, the move was less a mere suggestion and something that possibly should have been committed to. It never was, though, and the ICAO recommendation, which pushed for an overarching shift in the aviation sector toward metric units, remains to this day some half a century later.
That said, the move did come close to making it through. Namely, backing by the United States appeared to bring the shift as close to reality as it ever came. A presidential order and the passing of the Metric Conversion Act of 1975 by Congress seemed to have set the move in stone. However, momentum behind the national effort to make the change dropped off by the mid-1980s, and with it, any hope of a conversion across the world of aviation.
Cruising Altitude: How Low Is Too Low?
Elevating or descending? Cruising altitude is a direct result of safety, fuel use, and comfort in a myriad of ways.
Some Exceptions Where Meters Are Used
Much of the world does in fact use the foot when it comes to aviation and determining height. That is not to say all do, though, and there are some exceptions where pilots do have to switch to referencing their altitude in meters rather than feet.
Catch what other flight trackers miss
Emergency squawks, holds, NOTAMs — live signals, no signup.
Open tracker
Catch what other flight trackers miss
Emergency squawks, holds, NOTAMs — live signals, no signup.
Open tracker
China, for instance, uses the meter to express altitudes during flight. Mongolia, too, uses metric values for such purposes, alongside a string of Commonwealth of Independent States nations. But those that do are very much in the minority, and when it comes to alternating between the two, it can be a pain for pilots. In these cases, meters are used as the unit of measurement below what is known as the transition altitude, where pilots switch between standardized and localized air pressure settings. Above such altitude, flight levels – discussed later – remain the common practice, with these also based on feet globally.
Physical conversion cards are still sometimes used mid-flight upon crossing into metric airspace to this day, leaving it up to pilots to manually work out the correct altitude. Shanghai ATC clearing a flight to descend to 3,650 meters, say, would require the pilot to convert the value to 12,000 feet on the fly. While not so strenuous on its own, coupled with the high workload associated with landing at busy hubs like Shanghai, the additional task only adds to the complexity. Given a calculation that is off by 100 meters, a pilot would be some 328 feet off; the margin for error is incredibly fine.
Switching Would Cause Chaos
Having been the dominant unit of measurement for altitude since the inception of flight, feet have become so integrated in the majority of today’s aircraft that changing to meters would simply be out of the question. Realistically, most of the world’s aircraft are equipped with altimeters calibrated in feet. Pretty much every flight management system, approach plate, departure procedure, transition altitude, terrain clearance calculation, and Traffic Alert and Collision Avoidance System is built around feet.
In order for a shift to take place, changes would have to be made to almost all the world’s existing aircraft today. On top of this, almost all pilots and air traffic controllers would then have to be retrained and taught new operating procedures incorporating the use of the meter. A switch would also apply to the likes of nautical miles and knots, being ICAO’s other standard scales for distance and speed, as well.
All this goes to say, the change would just be too much of an inconvenience. Not enough countries use the meter for expressing aircraft height, so there’s no real justification for the rest to convert. Add questions about who would pay for all the retrofitting and retraining, alongside the massive safety implications, and the change is realistically out of the question.
Why Pilots Sometimes Avoid The Shortest Route On Purpose
Looking at a flight tracker often shows a wide range of interestingly shaped routes. They may look strange, but there is a method to the madness.
Vertical Separation Built On Feet
There remains one elephant in the room when it comes to the foot and aircraft height. So ingrained is the unit of measurement in aviation today that vertical separation between aircraft across most of the world is essentially built on 1,000-foot increments. This has been the case since 2005, with the introduction of the Reduced Vertical Separation Minimum (RVSM). Though largely a story for another time, what this means in plain terms is that certified aircraft and pilots can fly twice as close to each other than they used to be able to between the flight levels of FL290 and FL410, using a framework based on the foot.
Flight level itself translates to the mean height above sea level and is expressed in hundreds of feet. So in the case of the two flight levels mentioned above, FL290 and FL410 correspond to 29,000 and 41,000 feet (8,839 and 12,497 m) respectively. What this provides is a universal standard for pilots across the globe to determine where they are relative to others. In an attempt to further ensure fail-safe operations, the semicircular rule is also enforced globally. This sees aircraft heading in an easterly direction, wherever they are, operating at flight levels containing an odd number, like both of those mentioned above. Westbound aircraft then must adopt evenly numbered flight levels.
Why this will almost certainly never be changed is down to the same reason that it would be too inconvenient. More importantly, though, it could be excessively dangerous. Replacing it with a metric equivalent would require redesigning the entire vertical separation structure of global airspace simultaneously, which would be virtually impossible.
Safer And Simpler
At its core, the foot remains in use for reasons of safety. Whether that is the risk associated with any global attempt to switch to metric values or the simple fact that the meter is longer than a foot, and when it comes to precision and safety, using a smaller unit of distance allows for a reduced margin of error.
It is also simple for pilots to get their heads around. Calculating using feet to determine how many nautical miles from an arrival point one should have begun their descent, for instance, is rather straightforward. So, why mess with an established practice that, for all intents and purposes, works?
