At the Phoenix Aero Club we want to take advantage of the extensive knowledge bank of our current and former flight instructors. We intend to produce a series of handy tips that are available to PAC members. These tips and explanations will try to clarify any confusion you may have on a particular issue, and to help give you a deeper knowledge of certain issues, or at least to start a conversation with your flight instructor. These tips and hints will hopefully make you think twice and either refresh your knowledge or teach you something new!

Three such tips on various topics will be published below for public consumption, whilst PAC members will have access to a larger knowledge bank to help sharpen their knowledge! Join the Phoenix Aero Club today to access all of our instructors’ handy hints!


In aviation, icing conditions are those atmospheric conditions that can lead to the formation of water ice on the surfaces of an aircraft (including the propellor), or within the engine as carburettor icing.

CASA publishes a VFR Flight Guide which states, “Carburettor icing is of particular concern because, unlike airframe icing, the risk of ice build-up in the carburettor can be high even with no visible moisture and an OAT [Outside Air Temperature] of up to 38°C.

Carburettor icing occurs when the air temperature adiabatically decreases sufficiently to condense water vapour and for the localised air temperature to reduce below freezing.  Ice builds up as the chilled condensed water makes contact with localised surfaces, such as the butterfly valve and the venturi walls.  Carburettors experience additional cooling because of the evaporation of fuel.  Furthermore, the risk of carburettor icing is significantly increased at partial power settings (for example, when power is reduced during descent), because of the cooling effect of a partly-closed throttle butterfly.  [However, it is important to realise that carburettor icing can occur at any power setting].

CASA has published a specialised chart to measure carburettor icing probability based on known OAT and dew-point depression.  Dew-point depression is the difference between OAT and dew-point temperature and this information is available from an aerodrome’s AWS or in METAR/SPECI aerodrome meteorological reports.”

Please ensure you are all very conscious of the risk of carburettor ice over the coming months. Our policy is that Carburettor Heat must be applied whenever you reduce power to below 2000 RPM, no exceptions. This means all descents, circuits and anything in the training area.  Also, at the first sign of a drop in RPM, apply carby heat wherever you are. Please discuss management of carburettor icing with your Instructor for further information.

 Further information from the ATSB

First and Last Light

“FIRST LIGHT” and “LAST LIGHT” – ‘Night’ is that period between the end of the evening civil twilight and the beginning of the morning civil twilight. For all intents and purposes, first light should be construed as the beginning of civil twilight and last light as the end of civil twilight. The terms ‘sunrise’ and ‘sunset’ have no relevance when calculating daylight operating times for the VFR pilot.

NAIPS automatically computes first light and last light. This information can be provided through NAIPS Pilot Access, as part of a telephone briefing, from Flightwatch (AIP GEN 2.7).

Unless the pilot in command holds a command instrument rating or night VFR (NGT VFR) rating and the aircraft is appropriately equipped for flight at night, a VFR flight must not depart from an aerodrome:

    • Before first light or after last light (See Visual Flight Guide) and
    • Unless the ETA for the destination (or alternate) is at least 10 minutes before last light after allowing for any required holding.

High Voltage Warning Light on Cessna 172 Instrument Panel

The red warning lamp on the Cessna 172 Instrument Panel marked “High Voltage” is actually a warning light that means “Alternator Off-Line” and indicates that the battery is discharging. It will be ON during normal pre-start checks, but if it is ON when the engine is running, the alternator is not charging the battery.  If this happens, you should confirm discharge by checking the ammeter. The High Voltage warning light may be ON with the engine running as a result of High Voltage (due to the Overvoltage Sensor relay switching the alternator off-line), but can also be ON if the alternator belt has broken, or if the alternator is switched off. If the High Voltage light is ON when the engine is running, and the ammeter indicates discharge, this may be able to be fixed by cycling the alternator switch off and on.

The alternator switch is marked “DO NOT TURN ALTERNATOR OFF IN FLIGHT” as a CASA requirement because switching a working alternator off in flight (with a low battery voltage) can result in the alternator not coming back on-line when switched back on, if the battery voltage is insufficient to excite the alternator fields. If this occurs, turn off all non-essential electrical equipment (this is called “load-shedding”) and retry switching the alternator on.  Always do a full in-flight troubleshooting check in case your diagnosis is WRONG. If the alternator does not come on-line, you have about 30 mins of electrical power (with a fully charged battery) so return to the field and make an early radio call while radio is still working. On a long cross-country flight, turn all electrics off, including radios and navigation aids (by turning off the Master Switch) and stay in Class G airspace until approaching your destination where you will be able to have the problem fixed which is a priority. Revise the general “Communication and NAVAID Failure” procedures in ERSA Emerg AND the specific “VFR Communication Failure” procedures in ERSA for the aerodrome concerned.

Note that the engine runs normally even with a flat battery because the spark plugs are energised by the magnetos, not by the alternator and battery, but electrically driven flaps will not operate.

Always ask your instructor for further information or clarification on any information you find.

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