Boom/Aircraft Proximity-Detection System for De-Icing Operations

Aircraft de-icing operations prior to takeoff are crucial to ensure passengers security during cold weathers. Contacts between the boom and the aircraft must be avoided since it can lead to damages and delays. This article presents an ideal contact-free solution for this application.

____________________________________

De-Icing Operations

According to Canadian regulations any accumulation of ice and snow on grounded aircraft must be removed before takeoff and the reason for this is that even the smallest quantity of ice can result in a fatal crash. Airports are proposing a range of both curative and preventive measures but it is the pilot in command who holds the ultimate responsibility for determining whether his aircraft is free from contamination, and to ensure a safe flight. If this is not the case, the aircraft is subjected to a thorough de-icing/anti-icing before takeoff.

.
In the larger airports, de-icing (curative) and anti-icing (preventive) systems are implemented using trucks which were specially-designed for these activities. As illustrated in Figure 1, they are equipped with a nacelle which allows an operator to spray products over the surfaces to be treated through a nozzle (wings, stabilisers and fuselage).

Figure 1 De-Icing and Anti-Icing Operations at the Montréal Airport

Current Detection Technology

In order to avoid collisions with the aircraft, itself, during de-icing/anti-icing operations, the booms are equipped with mechanical proximity sensors such as those shown in Figure 2. They will immediately stop the boom before there is any contract with the aircraft.

.
This technology does not always prevent collisions, and sometimes the aircraft surface is impacted. If there is violent contact, the detector itself can damage the aircraft. There are many issues: costly structural repair, monopolisation of the aircraft during maintenance, flight delays and unhappy clients. On top of that, an investigation and a formal report are required when a collision occurs, even if the collision is only minor, and this leads to additional delays.

Figure 2 Mechanical Proximity Detectors on a De-Icing Boom

It is undesirable for any part of the truck or boom to touch the aircraft, so a contact-free solution is preferable. The range of the contact-free, proximity-detector must, at minimum, be one meter since this is the desired separation to be maintained between the de-icing nozzle and the aircraft for de-icing and anti-icing operations. When considering operational and environmental requirements for this application, it becomes apparent that ultrasonic detectors are an ideal solution.

Ultrasonic Proximity Detectors

Ultrasonic proximity detectors are contact-free sensors capable of detecting any kind of object regardless of its colour, transparency or composition. They all include an oscillator which is an electronic circuit producing a periodic signal whose frequencies range from a few tens to a few hundreds of kilohertz over a period of several milliseconds. A piezoelectric transducer receives this signal and then transforms the electronic energy into mechanical energy to produce an ultrasonic signal whose frequency is the same as that of the oscillator.

.
When an object is in proximity, the sound wave’s echo is detected and transformed into a digital or analog signal through variation of the current or voltage. In this way, these detectors can sense all kinds of materials in any type of environment at a range of several meters (Figure 3).

Figure 3 Ultrasonic Proximity Detectors – Principle of Operation

Some ultrasonic detectors have already been designed to be installed on booms, such as the VariKont L2 detector shown in Figure 4.

Figure 4 Pepperl+Fuchs VariKont L2 Detectors de Pepperl+Fuchs Installed on a Boom

The maximum angle of propagation of the ultrasonic waves is known by the manufacturers, so it is possible to calculate the surface covered by the detector and thus determine the number of sensors required for any given de-icing boom. Depending on the type of truck, between 5 and 11 detectors, installed on the boom’s lower edges, are required in order to ensure collision-avoidance.

Interference Risks

For this application, the detectors use ultrasonic frequencies of 85 kHz and 175 kHz. During de-icing operations, communications are also performed through waves. These waves, however, are electromagnetic or, more precisely, radio-electric, and are called “UHF” (Ultra-High Frequency) which range from 300MHz to 3GHz. There is no interference between these detectors, the ground communications and/or the control tower since two different types of waves are being used.

Conclusion

Currently, mechanical proximity-detection systems are being used and they detect aircraft surfaces through physical contact as pressure is exerted on the sensor. This technology could be improved.

.
A contact-free solution, based on the use of ultrasonic proximity detectors, will better anticipate collision. In addition, a multiplication of sensors installed on the boom will ensure reliable detection. Finally, this technology provides operators with more options. In fact, their commutation thresholds are programmable so they can sound an alarm at any given distance between the boom and the aircraft. The advantage of these kinds of sensors make their use feasible for de-icing and anti-icing operations.