In instrument we trust

Published On: June 29, 2019 01:25 AM NPT By: Hemant Arjyal

The most critical step in making aviation safer, as what it is today, was primarily due to setting up of “standard pressure” that governed cruising in the airways

Most find it baffling as how aircrafts fly long distances, safely and amidst crisscrossing traffic—seemingly under no control. If that was so, it would have resulted in frequent collisions or other types of midair calamities typically reflecting Kathmandu traffic scene where lack of patience rules supreme. It is not that drivers do not know the rules. It is the wanton disregard that has set the despicable trend which is getting worse by the day as more vehicles pour into our streets nonstop. But fortunately, saner minds prevail in the sky making it smooth and orderly. 

Air traffic was very slow to grow as there were not many who took risk flying in early years. Besides aircrafts were relatively short-range capable. But it grew at double-digit rates following the World War II until the oil crisis in 1973. This was largely due to technical innovation in aircraft design and subsequently improvements in jet engines. The introduction of turbo-pros (early 1950s), transatlantic jets (1958), wide-bodied and high by-pass engines (1970s) was largely responsible. Advances in avionics led to far reaching changes in cockpit design/layout and two-man crew instead of three. All these brought higher speeds, greater size, better unit cost control and lower fares that spurred an explosion in demand for air travel.

It can be said that pursuing an unnatural endeavor like flying largely helped instill discipline among pilots from the very beginning. Being cautious was a natural response to overcome associated fear. For any trainee pilot going solo for the first time must have had such notion driven harder into head as keeping the machine and himself safe solely rested on his shoulder alone. It was this that helped make flying safer than any other form of transportation.

As the air traffic began to grow and aircrafts started flying longer distances, some sort of order applicable worldwide, became necessary. Aerial routes had to be defined and delineated, mode of effective communication between the flying machine and ground stations had also to be set up. Then arose the need to have weather stations at the airports that provided data on wind conditions, local temperature and atmospheric pressure. As the airlines had to pass through the airspace of many countries en route a wider agreement between most became mandatory to make it seamless. The weather dimension grew even wider with forecasting becoming more trustworthy.

Standard safeguard
But the most critical step in making aviation safer, as what it is today, was primarily due to setting up of “standard pressure” that governed cruising in the airways. We were taught in school that a standard atmospheric pressure at the sea level was 760mm of Mercury (Hg), but in reality it is seldom as stable. As air pressure is directly linked with altitude, adoption of “standard pressure” (1013.2hP) helped to ensure that the flight level assigned by Air Traffic Controller (ATC) was always attained precisely as required. Every single aircraft, traversing in airways, climbs to its assigned altitude based on this benchmark. Flights below transition level are flown with different non-standard or local setting called QNH, which gets changed as deemed right by meteorology. All flights near around airport or part of the country fly with such settings. But they do not just rely on pressure setting alone at lower altitude for which a more accurate radio altimeter (RA) is used.

With standard pressure taking care of the vertical separation, it remains to be explained how the horizontal separation, which was no less vital, was achieved. And for which the humble magnetic compass became the standard instrument. Compass had been in use long before anyone had ever thought about air pressure. A compass rose is much like a school protractor, graduated in 360 equal divisions and is known formally as “whole circle bearing” (WCB). The four cardinal directions are 0/360° (N), 90° (E), 180° (S) and 270° (W). Depending on the flight heading, an aircraft obviously falls in one of the two halves (0-179° or 180-359°). The split may look odd but following example will help explain the reason behind. Consider two aircraft cruising on heading 179° and 180°, as the first one is required to maintain “odd” flight level (290, 310, 330 etc), the other “even” flight level (280, 300, 320 etc). So there is no question they will ever run into another mid sky even if appearing to flying on a converging track. Make the situation worse by putting them on a head on collision course; they will still miss each other by at least a 1000 ft. The only critical situation arises when an aircraft requests a change in cruising level, say, from 330 to 350 or higher to lower. The ATC will allow this only if there is no other conflicting traffic nearby flying at 340.   

For example, RA205 flying to Delhi had recently just passed Lucknow (LLK) at FL360 heading west at 502knots, coming from opposite direction was flight UTP9944 heading to Kunming (KMG) at FL350 and 469knots. The vertical separation between stood at 1000ft but they were approaching each other at 971knots (502+469) or roughly 30km a minute. Even if the combined speed looks horribly fast and separation too small, it is still considered safe enough given the reliability of equipment standardization. But as this rule is not applicable below the “transition level” the assistance of ATCs becomes ever crucial in guiding aircrafts as they come in or depart. For low level flights countries usually break WCB into four equal parts with each part having 89°. The rule here becomes, “odd” level for the first quarter followed by “odd+500” for next and so on making the vertical separation as effective.

How flights transit 
Next, it is time to explain how flights transit from one country to another, including swath of oceans under no one’s jurisdiction, so seamlessly. For this ICAO has designated areas as “flight information region” (FIRs) in which a flight information and alerting services are provided and managed by an air traffic services authority appointed by the ICAO. There are in excess of 300 FIRs spread around the world with bigger countries having more number of FIRs. Russia being the largest has 28, the US 26, China 10 and India four. Many countries do not like other’s FIRs imposed on them even if it is not supposed to reflect negatively on their sovereignty. 

Some countries let higher flight levels be governed by neighboring FIR by keeping lower level flights under their own control. It is no surprise there are about 114 individual country FIRs worldwide. Singapore has a huge area of sea to its northeast under its FIR, grossly disproportionate to its tiny size. Its responsibility is only limited in facilitating flow of air traffic in/out from FIA under its control to/from neighboring FIRs, all for the sake of making air travel safe and seamless. As airlines make money by transporting passengers and cargo, countries that provide and maintain en route navigation aids charge airlines for over flights passage. 

We cannot imagine that the first ever London-Brisbane flight in 1935 took twelve and half days. Nevertheless, it was still considered worth it, passage through high seas took several weeks longer. As for Perth-London flight it can be now done, nonstop, in about 17 hours flat. Being the first and only direct commercial flight in this sector, it highlights how innovation is spawning new frontiers for airlines to conquer. We cannot say much about God, but we have, unknowingly, bestowed greater trust in godly instruments.

Leave A Comment