Airplanes have brake pads

                                           The braking system

An aircraft basically has 3 brakes:

The airbrakes:

These flaps change the airflow on the wings so that there is less lift. By
the reduced lift comes from the effect of the weight (of the aircraft)
Wear and thereby the pressure on the wheels is increased, which leads to a better braking effect.
This is particularly important in the case of an increased approach speed because the
Lift is greater.

The thrust reversal:

The turbines rotate in the opposite direction as normal, this creates a force
which counteracts the direction of movement of the aircraft; this leads to deceleration
of the aircraft. The thrust reverser is used to support the wheel brakes.

The wheel brakes:

The mode of action here is the same as in any car: the rotation of the tires is prevented
(e.g. by brake pads) and thereby speed is reduced. To get an optimal
An ABS system is integrated to ensure braking. The way it works is about
as follows:

If it is recognized that the tires are spinning, the brake is (briefly) released, thus
the tires regain full grip. Even if the time in which the brakes are applied
this type is reduced, the braking distance is better in many cases and almost never
worse.

It is also important to mention that the commands from the pilot to the aircraft are only given to the on-board
Computer had to be handed over and this then - after going through one more or less
elaborate verification procedure - the devices switched or not. But the pilot hardly has
or no influence at all on the computer and it has the final say (What
is very problematic !!)

The release of the various braking systems was also monitored by the computer.

To the logic of the braking system:

The effective weight of an Airbus 320 when landing is approx. 58 tons, the touchdown
speed is in the order of 320 km / h.

In order for the airbrakes to be activated, the pilot must first activate the system. The
Airbrakes are extended as soon as there is a weight on the two rear landing gear
of> 6,300 kg or if the rotational speed of the rear wheels is a speed of
140 km / h above ground.

The thrust reverser is activated when the weight on both landing gear is> 6,300 kg.

The wheel brakes are then finally activated as soon as the rear wheels reach a rotational speed.
have a speed of 140 km / h.

The question now naturally arises as to whether there was a technical defect in the braking system or whether it was itself
the aircraft behaved correctly or how can the behavior of the system be
explain at all:
To do this, we first consider the period of 9 seconds in which no braking system reacts
Has:
Due to the strong aquaplaning, it is quite conceivable that the speed of the wheels will be less
than 140 km / h.

In addition, with increased approach speed (as in our case) the lift is greater,
this puts less strain on the landing gear. If you now assume that the
Aircraft has touched down a little to the side, i.e. initially only the right rear wheel and
the front wheel were on the ground, the case is perfectly realistic that on the left wheel almost
was no weight.

So it is also conceivable that there was neither enough weight on the rear wheels, nor the ones
Wheels turned fast enough.
After considering the specification, this then results for the components of the brake system
the following:

Airbrakes cannot be activated (because neither speed nor weight on the landing
frame is sufficient),
Thrust reversal cannot be activated (as there is insufficient weight on the landing gear
is), wheel brakes cannot be activated either (because the speed of the wheels cannot
is sufficient).

We now consider the period of 4 seconds in which no wheel brakes were activated
But airbrakes and thrust reverser were already activated:

This is the case when there is enough weight on the rear wheels, but the speed
the wheels are not yet sufficient. Aquaplaning was seen as the cause for this.

According to the specification, the behavior of the aircraft was more than understandable:
Due to the increased approach speed, which led to the lower weight on the wheels
and the aquaplaning, which led to a reduction in the contact of the tires with the ground, could
Computers do not "understand" that it is a landing.
The reason for this was not due to any technical problems with the aircraft, but to
a specification that was incorrect in this case (extreme case).