Reaction threshold (6000-9000ft)

Symptoms of oxygen deficiency start to show at this level, in the form of tiredness or exhaustion.

In the cabin of an aircraft the oxygen content is kept equivalent to a level of 6000ft or less, to prevent even those with the lowest tolerance from experiencing symptoms.

Disturbance Threshold (12000-15000ft)

At this level the symptoms are more serious. The lack of oxygen now also starts to affect our cognitive processes.

We start to lose the ability to think clearly and to make sound judgements.

We overestimate our abilities.

Critical Threshold (18000-24000ft)

At this level the density of air and oxygen content are only half of the value on ground.

More severe symptoms of oxygen starvation now also start to show.

Co-ordination of muscles is affected and the body will become paralysed.

Humans must leave this level as soon as possible.

In the even of depressurisation, the ACFT may stop its climb, request immediate descent or descend without warning.

If the problem cannot be resolved the crew will perform a rapid descent to below 10,000ft where passengers can breath unaided. The higher the ACFT the faster the rate of descent.

By doing this, the ACFT will descend through other levels and separation from other ACFT may be infringed.

These manoeuvres may cause injuries to passenger or crew.

ATC

In the event of pressurisation problems, REMEMBER:

Follow the ASSIST code of practice:

· Clear airspace directly beneath the aircraft

· Inform pilot about minimum enroute altitude

CREW

V. Electrical problems:

Electrical problems may be caused by failures one or more of the aircraft’s generators, a short circuit, or other technical deficiency. Lightning strike may also cause problems with the electrical systems.

Loss of electrical power is an emergency situation. Even though most aircraft can still function on reduced power, a possible complete power failure must be expected. Therefore, partial failure is also treated as an emergency.

When a pilot reports the aircraft to be an a standby power, remember most aircraft will have battery supplied electrical power for only 20-30 minutes, so urgent action by ATC is required.

Typical power supply systems:

Most modern transport aircraft have two generators and a battery for power supply. Smaller aircraft will have less backup and therefore lower redundancy.

In order to conserve power supplies, all unnecessary power-consuming systems shall be switched off. This may include, for example the transponder and internal & external lighting. As it must be expected, that all power supply could end, the flight may wish to continue under VMC. This may require level changes.

Landing at the next suitable aerodrome is the expected action in this situation. Read back may be limited to save energy.

If all generators are down, the battery will not be recharged and supply will be extremely limited. Only the navigational instruments will be working and even these may be limited.

Systems affected by electrical power supply problems are:

Electronic devices: transponders, computers, controls and indicators, sensors

Electrical heating:Galley, anti-icing

Lighting:Cockpit, cabin, exterior

Mechanical Power: pumps, valves

If the battery supply is exhausted there will be a failure of navigational systems, including the compass, and the pilot will have to work hard to fly the plane safely. Therefore, the aircraft will need all available navigational assistance, especially if it cannot remain in VMC.

As the workload in the cockpit is increased the crew may experience high stress levels. This could result in delayed responses to ATC.

ATC

In the event of electrical problems, REMEMBER:

· Follow the ASSIST code of practice

(See the ASSIST panel on the bottom left for further information.)

· Informing the supervisor

· Informing the landing aerodrome

SITUATION: General ATC actions to be taken if needed.

Be ready to assist the pilot by:

· Giving pilot suitable next aerodrome

· Giving the pilot RWY details as soon as possible: RWY in use, length, surface elevation

· Informing pilot of suitable vectors and position information

· Advising pilot to save energy

· Advising pilot to avoid IMC

SITUATION: If needed, ATC actions to be taken if all ACFT generators are out.

Be ready to assist the pilot by:

· Handing over ACFT to the local APP unit as soon as possible

· Avoiding all requests to pilot, and clearance which might increase the consumption of energy on board

· Phrasing ATC messages so that the pilot can answer them with a click on the mike button or just ‘Roger’ or ‘Affirm’

· If a primary radar detection is not possible, advice pilot to switch transponder to STBY now and then, to save energy

· If the NAV-Instruments are switched off, give radar vectors and position information to the pilot

CREW