Too hot to fly full? – Summer heat could force airlines to reduce aircraft loads

Airline passengers could find themselves bumped off flights, separated from their luggage or facing delays this summer as extreme temperatures threaten aircraft performance at Johannesburg’s OR Tambo International Airport and other high-altitude airports.

South African Airways (SAA), Airlink and LIFT have confirmed that exceptionally hot conditions could force airlines to reduce cargo, baggage and passenger numbers to get aircraft airborne safely.

The El Nino weather system currently in play has served up some scorching days.

SAA on aircraft performance

SAA spokesperson Mphilo Dlamini said the carrier’s aircraft performance modelling showed that an Airbus A330’s maximum permitted takeoff weight could fall by as much as 20 tons in temperatures between 25ºC and 40ºC.

Larger aircraft operating long distance routes could face even greater restrictions.

Dlamini said managing extreme heat involved more than removing passengers or luggage.

Airlines must consider aircraft performance, fuel requirements, departure times and ground operations before restricting passenger numbers.

He said an Airbus A320 could depart at about 77 tons at 25ºC, but its permitted takeoff weight could fall to 73.5 tons at 40ºC.

For an Airbus A340, the difference is more dramatic, dropping from 261 tons to 227 tons, a reduction of 34 tons.

“Long-haul sectors departing Joburg are exposed to more extreme heat than shorter sectors, particularly when high fuel requirements coincide with high temperatures,” Dlamini said.

SAA’s analysis showed an A340 carrying 80 tons of fuel could have about 44 tons available for payload under cooler modelled conditions.

At 40ºC, this could fall to just 10.5 tons.

‘High temperatures reduce air density’

LIFT chief pilot of flight operations Warren Penney said extreme heat reduces air density, affecting engine thrust and the ability of aircraft wings to generate lift.

“High temperatures reduce air density, resulting in reduced engine thrust and aerodynamic performance. This can increase takeoff distances and reduce climb performance,” said Penney.

“OR Tambo’s elevation of about 5 558 feet compounds this effect, making hot weather departureparticularly challenging.”

He said temperatures above 30ºC warranted particular attention, although no universal temperature automatically triggered weight restrictions.

“Performance is calculated for every departure based on temperature, pressure, wind, runway conditions and aircraft weight,” Penney said.

An Airlink spokesperson said the phenomenon, known as density altitude, affected everything from small private aircraft to large commercial jets.

“The higher, hotter and more humid the conditions are on the ground, the thinner the air.

“It’s critical because thin air compromises the lifting capability of an aircraft’s wing and determines the aircraft’s takeoff distance with its load of passengers, luggage, cargo and fuel,” the spokesperson said.

“When the required takeoff distance is longer than the available runway, then the aircraft must be made lighter so it can take off and climb safely.”

Cargo removal

Airlink’s spokesperson also said airlines would generally remove cargo first, followed by adjustments to fuel loads where regulations permitted.

Baggage restrictions and removing passengers would follow only if necessary.

Critical cargo, including lifesaving medication and human organs destined for transplants, would not be offloaded.

Airlines could also move departures to cooler mornings or evenings, although Airlink warned that delaying scheduled services could disrupt connecting passengers and subsequent flights operated by the same aircraft and crew