Flight International - 04

Environment Airlines
“When we did the transatlantic
flight achieving the rendezvous
was relatively easy; now we want
to see how fello’fly is deployable
at a large scale”
Jonathan Beck Fello’fly project leader, Airbus
However, there are plenty of
practical considerations to be
hammered out before Geese reaches
that point.
For example, where is the ideal
point during the cruise phase for
the two aircraft to join? “We want
it to be as soon as possible to save
as much energy as possible, but we
have to account for the delays that
will happen for operational reasons,”
he says. In other words, there will be
a natural lag caused by all the steps
required – the pairing, transmission
of the changed flight-plan to crews,
its validation by air traffic control –
before the jets link up.
Managing separation
“When we did the transatlantic
flight [in November 2021] both
aircraft departed from Toulouse
with little separation between
them, so achieving the rendezvous
was relatively easy; now we want
to see how fello’fly is deployable at
a large scale,” adds Beck.
There is also the thorny question
of how to decide which aircraft is
the leader and which is the follower.
While a heavier aircraft would
arguably benefit the most from
being in the trail, it also generates
bigger vortices, creating more lift
for its partner, and so would be
better positioned in front.
While the decision in some cases
may come down to a commercial
agreement between carriers, Beck
says other factors may come into
play, such as whether both crews
are trained to fly in either position.
Crucially, Boeing has been recruited
to the project to ensure “we
align the concept of operations
across OEMs”, says Beck.
“Part of the discussion we want
to have is around the interoperability
of different aircraft types for
formation flying.”
A suitable fello’fly partner should
have a similar cruising speed and
altitude, says Beck, with the basic
rule that one aircraft works well
with another of the same type. But
some “cross-combinations” also
work, such as the A350 and A380,
and he sees “some potential” for
co-ordination between the A350
and the Boeing 787.
Launch of the system will be with
the A350, because “it’s our most
Activity is focused on using
a pair of A350 widebodies
recent aircraft with the best connectivity
and best avionics systems”,
but in the longer term there is “no
reason” it could not be extended to
the A330neo or even A321XLR.
Theoretically, the benefits of
fello’fly could extend to any number
of aircraft in a suitable formation,
but in practice this will be
confined initially to just a pair “because
operationally it is already
very complex”, says Beck.
Contrail formation
In addition to the fuel-saving – and
therefore carbon dioxide emissions
reduction – benefits of the VRS, it
could also have a positive impact on
contrail formation, says Beck, which
will be assessed by Germany’s DLR
aerospace research institute.
Outside of the Geese project,
Airbus is evaluating what changes,
if any, will be required to the aircraft
themselves, along with certification
assessment, to enable a commercial
roll-out of fello’fly.
“It will take a few more years to
assess whether it fits with the A350
system with as little modification
as possible,” he says. Airbus will
also work with European, and later
US, regulators on the certification
aspects of the project.
Beck is hopeful that changes can
be confined to a software update
rather than any retrofit programme.
As tested, the flight-control and
auto-thrust systems on the trailing
aircraft maintain its position laterally
and vertically relative to the
vortex and between the jet in front.
“We are able to maintain a globally
constant separation between the
two aircraft,” he says.
Initially developed by the airframer’s
UpNext innovation arm,
responsibility for fello’fly has since
transferred to Airbus’s commercial
aircraft unit. ◗
April 2023 Flight International 41