Aviation Specials – May 2018

Extreme Airports // 59

COURCHEVEL

Departure

Once we were ready for departure, we

taxied the aircraft on the fl at section

and turned onto the runway heading.

We then put the propellers into reverse

pitch and rolled backwards. We were

aiming to get as close to the mountain

as possible, while keeping a close eye on

Patrick’s hand signals – we wanted to use

absolutely every metre of the runway.

After Anne e radioed “runway is

clear” we could get moving. But before

describing exactly how we took off , I

should expand on a few details. When

the Dash 7 starts moving with the

thro les and all four engines are set

to full power, it will head in the desired

direction thanks to the traction of the

nose landing gear. However, if one of the

outer engines loses power as the aircraft

starts to roll forward, it will turn in the

direction of the failed powerplant and

leave the runway. This happens because

the nose wheels don’t have suffi cient

authority to counter the swing, and the

aircraft is not moving quickly enough for

directional stability from the tail surfaces

to come into eff ect. The rudder fi nally

becomes eff ective at 60kts, a speed

known as Vmcg [minimum speed required

for directional control on the ground].

The only solution that enables

directional control to be retained below

Vmcg after an outer engine failure is

to abort the take-off. However, this is

complicated by another decision speed,

V 1. If V 1 has not been reached when the

engine fails, the take-off must be aborted.

Above V 1 , the departure must continue,

come what may. After we reach V 1 , we

don’t even feel it if we lose an engine –

we have directional stability, the steep

runway helps the aircraft accelerate, and

the Dash 7 will take to the air.

And that’s where we came to a

dilemma. We couldn’t bring the aircraft

to a standstill on the steep runway, so

aborting the departure was unthinkable.

What could we do if one of the engines

failed while we were doing less than

60kts? How could we ensure the aircraft

travelled in a straight line? We had to

‘outsmart’ Vmcg.

Ernst came up with an idea using his

slide rule. Firstly, we would park in the

take-off position with the brakes on. Then

the captain would advance the thro les of

the inner two engines to 100%. After that,

the power of the outer two engines was

set to just 60%. In this confi guration the

ABOVE: A Tyrolean

Dash 7 shares

the apron with a

King Air and a Siai

Marche i S-205.

(Markus Herzig)

BELOW: When

Tyrolean Dash

7s were regular

visitors, Anne e

had coff ee ready

for the aircrew.

(AirTeamImages.

com / Paul Marais-

Hayer)

56-62_Courchevel.indd 59 11/05/2018 12:14