Explained: How higher-than-usual temperatures are grounding flights at Leh

medium nocaption112143078An IIT professor attending an event on climate change and corrective measures in Ladakh was among the many who found his flight on July 28 cancelled due to the high temperatures at Leh airport.Professor Chetan Solanki reached Leh airport for the 1pm IndiGo flight to Delhi only to be told that the flight had been cancelled due to high temperatures. Temperatures have exceeded 32 degrees Celsius at the airport over the past few days. "The surprise was not the flight cancellation but the reason for which it was cancelled - high temperatures,” he said.As temperatures soared at the high-altitude airport, airlines have been cancelling flights, with four flights cancelled on Tuesday (July 30). Around 16 flights have been cancelled since July 27. In a statement, IndiGo said its "flight operations to and from Leh have been impacted due to the prevailing high outside air temperature in Leh, which is beyond the airline's control".Why high temperatures hit aircraftAirport officials said this is perhaps the first time that a weather event has affected flights. The airport sees 15-16 arrivals and departures daily. “This is perhaps the first time that an extreme weather event [heat in high altitude] is causing flight cancellations at Leh airport. We cannot recall any time in the past something like this happening for three days in a row,” said airport sources.In the case of the Leh airport, the air density and temperature play important roles. Air density decreases with increase in altitude, which is why mountaineers rely on oxygen cylinders at heights above 14,000 feet. The Leh airport is at an elevation of about 10,700 feet, where the air is much thinner than the Delhi airport, which is at about 770 feet. Another factor that decreases air density is temperature - the higher the temperature, the lower its density. A combination of these two factors spells trouble for aircraft.Low air density degrades engine performance. The A320s and B737 jet engines take longer to rev up and reach lift-off speed, thus consuming a longer length of runway during take-off.Here’s a video that explains how it works https://youtu.be/cwz5XgcUfIAThin air also affects aircraft performance post take-off during the climb phase and then again, when landing as the aircraft needs a comparatively higher approach speed to generate enough lift to stay afloat. "High temperature forces weight restrictions on aircraft. Last week, we had the air traffic controller report a temperature of 37 degrees Celsius, which is too high for Leh operations," said an airline commander, on condition of anonymity. High temperatures at that altitude means aircraft engines cannot develop the thrust required to take off with commercially viable load. medium nocaption112143143Heat and height are also a deadly cocktail for engines. However, airports like Delhi see wide body aircraft take off for long haul flights even at 45-47 degrees Celsius as Indira Gandhi International Airport (IGIA) is only 770 feet above mean sea level, pilots explained.Senior commander Capt Amit Singh said: "Temperatures above 36 degrees C at the Leh airport is akin to taking off from a runway that's at an altitude of 16,000 feet, which makes the aircraft incapable of taking off safely." 112142978How heat is affecting flights globallyWhen airlines realise that Leh temperature could cross 32-33 degrees Celsius at the scheduled time of departure, they cancel the flights - meaning do not send the aircraft to Leh or divert it to some other place if already enroute. They do this because after landing, the aircraft could get stuck there till the next morning and will not be able to do all the other routes it was supposed to. Or it could have to fly back with hardly any passengers and baggage. The Leh airport already sees flight operations only till around 1pm as tailwinds later in the day get too strong to permit aircraft movement.But it’s not just Leh that’s affected. Globally flights are being affected by heatwaves and high summer temperatures affecting flight operations. In the US, higher temperatures are believed to be getting airlines to reduce the weight of the aircraft before takeoff. This could mean offloading of baggage or flyers or burning of fuel before takeoff. These measures could cause delays that anger passengers. One airline also made headlines after multiple aerated drink cans exploded on board flights because they weren’t stored in refrigerators. Professor Solanki, who is on unpaid leave from work and left his Mumbai home in 2020 on an 11-year 'Energy Swaraj Yatra' to create awareness about climate change, said the fact that he was a victim of global warming at Leh was “unimaginable”. “No one will be spared the impact of climate change. Today, I have become a victim. Everyone should know their turn and their children's turn will come,” he said.Reporting by Manju V and Saurabh Sinha