By Girish Linganna

Jan 17: WINTER IN DELHI AND DENSE FOGS have become almost synonymous. As many as 53 flights were cancelled while Delhi airport grappled with fog and operational issues on Wednesday, according to the Delhi Airport Flight Information Display System (FIDS) operational issues, even as 21 scheduled domestic arrivals, 16 domestic departures, besides 13 international departures and three arrivals, were cancelled.

Between December 24 and December 28, a large number of flights had experienced delays and 58 of them were diverted due to poor visibility at Delhi airport. This issue also occurred on the following Sunday and Monday. According to an airport source, about 50 of these diversions happened because the pilots were not trained to handle dense fog conditions.

Fogs pose significant challenges for pilots during landing and take-off due to substantial reduction in visibility. This makes it extremely difficult to see the runway and other crucial visual markers necessary for safe landings and take-offs. Pilots require advanced instruments and specialized training to effectively land aircraft during foggy weather.

Aviation experts believe that flight delays during winter due to heavy fog in Delhi are caused by two primary factors

• Lengthy training times and
• Insufficient numbers of pilots trained to fly in foggy conditions

Captain SS Panesar, a former pilot and ex-director of Flight Safety and Training at Indian Airlines, said there was currently a widespread shortage of pilots in the industry. He also noted that, among these pilots, only a few were trained to fly in foggy conditions.

MINIMUM VISIBILITY STANDARDS
Minimum visibility requirements, commonly referred to as ‘minimums’, are established for safe landing. These requirements vary depending on the specific airport, aircraft equipment and pilot training and qualifications. While general visibility thresholds exist for normal conditions, more sophisticated systems, such as the Category III (CAT III) Instrument Landing System (ILS), greatly reduce these thresholds for low-visibility operations.

Under Visual Flight Rules (VFR), pilots need clear visibility of at least 3 miles (4.8 km) to see the runway and manually control the aircraft. Instrument Flight Rules (IFR), which include standard instrument approaches like the ILS, have varying minimum visibility requirements ranging from half a mile (0.8 km) to two miles (3.2 km) depending on the aircraft’s approach category and airport procedures.

For CAT I ILS approaches, pilots generally require a minimum visibility of half a mile (0.8 km) and a decision height of about 200 feet to determine whether to continue the landing or not. More advanced approaches, such as CAT II and CAT III ILS, permit landings in even lower visibility conditions. CAT II approaches typically require approximately a quarter-mile visibility, while CAT III approaches enable landing in almost zero visibility. The exact requirements for CAT III approaches depend on the sub-category (a, b, or c), along with specific aircraft and airport equipment.

These guidelines are general and can vary depending on airport regulations, aircraft equipment and pilot certification levels.

ILS APPROACH TYPES
CAT I, CAT II, and CAT III do not refer to specific aircraft equipment, but rather designate the types of ILS approaches an aircraft is certified to perform. The ability to conduct these approaches depends on a combination of the aircraft’s equipment and the pilot’s training and certification. For instance, CAT III approaches require advanced navigation and autopilot systems on the aircraft, as well as specialized training and certification for the pilots to perform low-visibility landings. Pilots must participate in training programmes like CAT III, which helps them guide the aircraft during descent and landing when in thick fog or low visibility conditions.

CAT III ILS approaches are further categorized into three sub-categories—CAT IIIA, CAT IIIB and CAT IIIC. CAT IIIA permits landing with a minimal decision height of approximately 50 feet and a Runway Visual Range (RVR) of at least 700 feet. CAT IIIB allows even lower decision heights below 50 feet or none at all, with an RVR as low as 150 feet. The most advanced, CAT IIIC, allows for landings in zero visibility without specified decision heights or RVR minimums. However, CAT IIIC approaches are rarely used due to the high level of advanced systems and specialized equipment required on both the aircraft and at the airport.

Airlines need to plan ahead and schedule flight simulator sessions well in advance for pilots to undergo specialized training for fog flying, particularly for CAT III approaches. Flight simulators are often in high demand for regular training to ensure that pilots maintain up-to-date licences. These simulators play a crucial role in providing realistic training scenarios for pilots to navigate low-visibility conditions effectively.

Ameya Joshi, an aviation expert and the creator of the aviation blog ‘Network Thoughts’, told Business Standard that CAT III training is very time-intensive for airlines as the simulators that are required are usually reserved ahead for regular training sessions. Getting a booking for these simulators is not easy and they are often unavailable. Joshi mentioned that, after the pandemic eased and flights restarted, there was a shortage of simulators. Most were already booked for pilots needing mandatory training to renew their licences. Because of this, the CAT III training, which also relies on these simulators, faced delays.

Additionally, the limited number of pilots in the industry might restrict airlines from sending all their pilots for such training sessions. When a pilot undergoes training, they have to be taken off their regular duties, which can affect the airline’s commercial operations as fewer of them are available for flights. Captain Panesar mentioned that airlines usually would not favour this approach.

Besides the significant time required for pilot training and the period they are unavailable for duty, training all pilots for foggy conditions can be costly for airlines. Additionally, foggy weather typically only occurs for a brief period each year and is mainly confined to major northern airports like Delhi, an industry insider noted. The source, who chose to remain unnamed, mentioned that training programmes could cost an airline about Rs 500,000 per pilot.

Joshi echoed this sentiment, noting that fog is primarily a concern in Delhi. He explained that airlines might consider the limited number of extreme fog days annually and conclude that investing in extensive training could be an added expense. Therefore, they might opt to manage operations during these few days instead of extensive training.

Joshi points out that, when visibility drops at airports, air traffic movement slows down, leading to fewer take-offs and landings. This results in aircraft having to wait or ‘hold’ in the air before they can land. Even if the pilot and runway are equipped for CAT III conditions, planes might still have to divert if they cannot hold any longer due to fuel limits. He said passengers often bore the brunt of these delays caused by such situations.

CAT II, CAT III TRAINING
Captain Panesar detailed that pilots need a minimum of 2,500 hours of flying experience for the pilot-in-command and 500 hours for the co-pilot to qualify for CAT II or CAT III training. After completing at least three hours in a CAT II simulator, pilots can then do a two-hour session focusing on CAT III ILS approaches. Only after successfully completing an actual landing in CAT III weather conditions do pilots receive CAT III certification. Panesar further explained that, for CAT III B, the visibility required for an aircraft’s landing and take-off ranges from 50 to 174 metres. In contrast, for CAT III A, it is between 175 and 299 metres.

Delhi airport possesses two runways compliant with CAT IIIB standards with one currently undergoing maintenance. Once it is operational, Delhi airport will have both CAT III runways functioning, which is anticipated to enhance conditions at the airport significantly.

INDIGO’S RESPONSE
Only IndiGo among the airlines seems willing to talk about the number of pilots trained for CAT III compliance. The airline has enough pilots qualified in CAT III to ensure smooth operations during the winter season. As the largest airline in India, operating over 2,000 flights daily, the number of their flights that were diverted was relatively small. The airline is committed to reducing passenger inconvenience caused by weather-related disruptions. However, other airlines are tight-lipped about the number of their pilots who were certified in CAT III.

A passenger on a Goa-Delhi flight shared his experience, stating, “On my return to Delhi, shortly after the pilot announced and instructed the cabin crew to get ready for landing, we ended up flying around for about 20 minutes, likely because of heavy fog. This resulted in our landing being delayed by half an hour.”

(The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach out to him at: girishlinganna@gmail.com)