The aircraft refuelling safety system “Hydrant Guard” was developed at the request of a major oil company following a series of incidents involving impact damage to hydrant connections during the refuelling process as a result of heavy traffic activity around aircrafts. Major airports refuel aircraft using an underground pipe system where fuel is supplied under high pressure to a hydrant located in the ground at each aircraft stand position.

The largest fuel tanker you will see on the motorway carries 38,000 litres - it would take 5 tankers to fuel a jumbo jet (180,000 litres). Modern international airports use underground high-pressure systems for refuelling aircraft. A connection is made between the underground network and the aircraft via a truck. It is this connection that is most vulnerable during the fuelling process. If a collision with another vehicle did occur and cause a fuel leak, it is not a simple matter of automatically shutting down a valve. A simple fracture in an above ground fuel conduit can therefore cause an uncontrolled gusher of fuel, which will almost certainly catch fire. The potentially catastrophic consequences of this happening close to fuel-laden aircraft need no elaboration.

Hydrant Guard is a fully patented stand-alone proactive system which shuts off the fuel to an aircraft when it detects an obstacle approaching. There are no recognised or acknowledged competitors within this product field. The prototype product has undertaken and successfully completed field trial evaluations with Shell at Gatwick Airport and has received the unqualified support and acceptance by the airport authority. To date £315,000 has been invested, including a SMART award of £60,000. The target market is the major re-fuelling operators, various safety committees and airport authorities worldwide.

Aircraft refuelling systems in use at most substantial airports incorporate an underground hydrant system including a network of fuel storage tanks buried in the airport apron.

The storage tanks communicate through pipe work and valves in a ring main system leading to a plurality of refuelling pits.

Each refuelling pit contains a valved pit head and a removable cover that, when in place, lies flush with the surrounding surface of the apron.
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When removed the cover permits access to the pit head so that a nearby aircraft can be refuelled by fuel flowing through the pit head - 

The hydrant dispenser is positioned adjacent to the aircraft’s refuelling point.  It is connected to the aircraft by a flexible pipe, and to the pit hydrant by another pipe or hose.

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Accidents can happen on airport aprons and if they do, they can have serious consequences in view of the presence of fuel-laden pipes and adjacent fuel-laden aircraft.

The vehicles and machinery used on airport aprons are often large with invisible extremities, eg.  truck with baggage loader, these vehicles are very difficult for there operators to position accurately.

This increases the risk of collision with refuelling equipment during refuelling.

Aircraft refuelling takes place in an environment that is often noisy and physically demanding, making it difficult to hear shouted warnings that a collision is imminent.

All these factors contribute to the likelihood of a fuel pipe being snagged and fractured, or of the coupling between the pipe and the pit head being knocked and the seal broken.

 The activity around an aircraft

The safety Issues

The most likely section in a refuelling network for a collision to occur and cause a fuel leak is in the link between the hydrant dispenser and the refuelling pit.

The coupling at the pit head and the refuelling pipe that leads from the coupling to the hydrant dispenser do not rise much above ground level and are relatively small compared to the scale of the surrounding machinery making them easy to miss.

It may be thought that even if a collision did occur and cause a fuel leak, it would be a simple matter of automatically shutting down a valve, unfortunately this is not so.

It is not practical for the pressure control mechanism of the system to differentiate between a normal drop in fuel pressure that occurs during refuelling and a pressure drop that might have occurred due to a leakage in the refuelling network.

 The pressure control mechanism of the system will switch on additional pressurisation pumps in an attempt to restore fuel pressure in the ring main system thereby worsening the already dangerous situation and pumping even more fuel to the site of the leak.

A simple fracture in an above ground fuel conduit can therefore cause an uncontrolled gusher of fuel, which will almost certainly catch fire.

The potentially catastrophic consequences of this happening close to fuel laden aircraft need no elaboration

Current Practice

Current practice to prevent such accidents involves placing one or more warning flags and warning cones around the vicinity of a refuelling operation when the hydrant dispenser has a live fuel connection.

Further practice involves providing the fuelling operator with a lanyard and air switch that can be triggered in an emergency to close the pit head valve and shut off the fuel supply.

The operator must therefore keep a close watch for moving vehicles around the aircraft and the refuelling area, so that if the operator fears a collision may occur, he pulls the lanyard in an attempt to shut down the refuelling pit before the collision actually happens

Problems With Current Practice

The current practice as described is unsatisfactory as it relies upon alertness of the refuelling operator and human intervention to pull the lanyard in time.

It can fail if the operator is incapacitated, slow or unobservant, and also the lanyard itself might not work in an emergency situation.

An incident occurred in 1998 at Manchester Airport when a baggage truck collided with a fuelling hydrant, and the wheel of the baggage truck trapped the lanyard.

In the USA an average of one incident  occurs each month.

 Pit heads do have a fail safe design but it is possible that a major collision could prevent the lanyard closing the valve ….. effectively disabling this failsafe.

The Solution

Functionality

When the system is armed the following levels of protection apply:
Visual Protection … high brightness flashing led’s mounted on the protection cone, the flashing frequency increases as obstacle moves closer to cone.
Audible Protection … 120db sounder activated when obstacle is within 40cm of protection cone
System shutdown … Pit Head shutdown when obstacle within 5cm

The system in operation

• Hydrant Dispenser Arrives
• Operator couples fuel lines to aircraft
• Fuel Lines connected to underground Hydrant
• Safety Cone Positioned and Connected

Description of protection system

• The system is housed in a free-standing cone, it comprises a pneumatic sequencer initialised by the application of an external air supply (min 55 p.s.i.) from the hydrant dispenser and a power supply of 24v DC
• A warning siren and flashing lamps in sealed units are incorporated. 
• Alarm activation and pit shutdown is triggered by  two types of sensor:

1] Ultrasonic sensors (Three devices covering 360degrees) triggering at a range of 0.9 metre *

2] Capacitive sensor system operating at 5cm range

*The ultrasonic sensors will not shut down the pit head, they are intended to warn obstacles within 0.9 metres of the live fuelling pit by audio and visual alarms.

Operating Sequence

1. With the unit positioned over the fuel hydrant, the fuel lines to the support vehicle are connected.�
2. The operator next connects the air couplings to the input and output connectors on the side of the cone.
3. The electrical supply to the unit is fixed using a hard coupled style connector and the supply protected by an EEX e certified Fuse.  The supply must be capable of supplying 24 DC Volts at a max current of 3 Amps. The six lamps will flash and the internal siren will initially sound, showing that the unit is powered ready for use.�
4. When refuelling is ready to commence and air is applied by activation of the dead man switch, the system will arm and the lamps will flash slowly indicating the Armed State.
 

Alarm Modes

1.  Ultrasonic sensors detects a person or object within 0.9 metre and within their field of view, the lamps will flash rapidly.  No fuel shutdown functions will operate. The lamps will revert to slow flashes if the person or object are moved out of the sensing range
2.  When the obstacle is within 40cm of the cone the 120db sounder activates no fuel shutdown functions operate.
3.  When the capacitive sensor detects an obstacle within 5cm of the top case, the air supply is removed and the pit head shuts down

Interested parties should contact MD Michael Leigh for a full business plan and further information.