At 6:45 am Thursday morning, two of United Airlines’ biggest planes

UAL
must leave Chicago for Tokyo. Neither will carry passengers.

Four more flights will depart the same day from Los Angeles and San Francisco to Tokyo, also without passengers. Instead, they will all be carrying vital medical and commercial cargoes.

Passengers can still travel to Tokyo with United. But while there are more than six daily freight-only flights to Tokyo, there is only one passenger flight.

Weekly intercontinental passenger and freight flights only on American Airlines and United Airlines: April 21-27

On United’s intercontinental network, freight-only flights outnumber passenger services. Over the next week, United is planning 42 long-haul international passenger flights, but 95 freight-only services, according to its schedules.

Likewise at American Airlines

AAL
, which provides for 17 passenger services but 23 cargo flights only. Delta Airlines

DAL
did not make their full schedules available.

It was almost unfathomable before COVID-19 for an airline to fly an empty passenger plane just for cargo.

But the sharp reduction in passenger flights has also removed the cargo capacity that was previously available under the passenger cabin. About half of the world’s cargo flies in the holds of passenger planes, and the other half on dedicated cargo planes, which are now generally at their peak.

MORE FORBESCargo planes roar to life, reaching record utilization as coronavirus creates urgent demand for air cargoThrough Will horton

In addition to humanitarian needs, the lack of capacity has seen freight rates increase. The inefficiencies of flying an airplane without passengers are offset by the fall in the price of oil. US airlines are fully benefiting from falling fuel prices as they do not have fuel hedging contracts, unlike European and Asian airlines which are typically forced to purchase fuel at around $ 60 a barrel.

Last week, U.S. airlines received advice from the Federal Aviation Administration on how to move cargo into the cabin of the plane, either on empty passenger seats or by removing seats. Airlines in Asia and Europe are already carrying cargo on empty seats.

MORE FORBESCargo in an airplane cabin? You will need a flight attendantThrough Will horton

Air Canada recently began removing passenger seats on three 777s to make room for more cargo. Airlines like Lufthansa are planning to do this as well while Cathay Pacific and Air New Zealand are studying it.

MORE FORBESHow Air Canada Quickly Turned 777 Passenger Jets Into Quasi Freighters To Carry Medical SuppliesThrough Will horton
MORE FORBESThese airlines will then remove seats to carry goods and medical supplies on passenger planes transformed into freighters.Through Will horton

Cargo-only flights from US airlines started out as a few ad hoc services per week, but are now gaining in regularity.

Cargo-only flights are increasing not only in frequency, but also in footprint. American Airlines added Asian cities including Hong Kong and Seoul.

United launched cargo flights only to Chengdu and Shanghai, complementing the service to cities like Brussels and Tel Aviv which have large pharmaceutical industries.

But overall, Asia dominates, accounting for 55% of United’s only cargo flights, and an even larger share considering distance and flight capacity. United tend to use their larger 777s and 787s towards Asia, while European destinations receive smaller variations of their widebody 787.

American operates the smallest long-haul network of the largest US airlines, operating only one daily flight to London from Dallas and Miami, and three weekly flights to Tokyo from Dallas. While Asia accounts for 18% of American’s international passenger network, it accounts for 61% of its cargo flights alone.

Freight has always been more dynamic than the relatively constant passenger side of air travel. Airlines may change aircraft types daily in response to demand. Flights can be added at short notice.

Demand for cargo-only flights is expected to decline as rising medical needs decline and airlines add more passenger flights. Although United recently postponed numerous passenger flights that it planned to resume in May, it tentatively expects clear growth.