On the odd occasion during my time on this forum I have noticed a few questions emerge relating to simple aviation 'rules of thumb'' I am writing this topic in the hope of it being pinned for reference to any future questions that may come up. I will add as many as I can, however feel free to add your own by contacting myself or a mod where they will be edited into this post. This post covers the basics of pilot reference including Abbreviations and their meanings, conversion factors and of course as the title says, general aviation rules of thumb.

[NOTE] All abbreviations, rules of thumb and conversion factors are derived from the current practices within Australia. Although similar, there are significant differences to the practices in other countries. I will do my best to include as much universal content as possible, but as I said feel free to add more.

Abbreviations
Contained in this section are the many aviation abbreviations used commonly in modern aviation...

AAL - Above aerodrome level-----------------------------------MHz - Megahertz
AGL - Above ground level----------------------------------------NDB - Non-directional Beacon
AI or AH - Artificial indicator or artificial horizon------------NOTAM - Notice to all airman
AIP - Aeronautical information publication------------------NVFR - Night visual flight rules
AMSL - Above mean sea level--------------------------------- NVMC - Night visual meteorological conditions
ARFOR - Area Forcast--------------------------------------------OCTA - Outside controlled airspace
ASI - Airspeed Indicator------------------------------------------PAX - Passengers
ATC - Air traffic control--------------------------------------------PIC - Pilot in command
AVGAS - Aviation gasoline--------------------------------------POB - Persons on board
BAK - Basic aeronautical knowledge------------------------POH - Pilots operating handbook
CASA - Civil aviation safety authority--------------------------PPL - Private pilots license
CAVOK - Ceiling and visibility OK-----------------------------PRD - Prohibited, restricted and danger areas
CFI - Certified flying instructor---------------------------------------PSI - Pounds per square inch (pressure)
CG - Center of gravity----------------------------------------------PTT - Press to talk
CHT - Cylinder Head temperature-----------------------------PVT - Private Category
CIR - Command Instrument rating-----------------------------QNH - Local altimeter (pressure) setting
CPL - Commercial pilots license------------------------------RIS - Radar information service
CTA - Controlled area--------------------------------------------RBI - Relative bearing indicator
CTAF - Common traffic advisory frequency-----------------RMI - Radio magnetic indicator
CTZ - Controlled zone
DA - Density Altitude
DI or DG - Direction indicator or directional gyro
EGT - Exhaust gas temperature
ELT - Emergency locater transmitter
ERSA - En route Supplement Australia
ETA - Estimated time of arrival
FIR/FIA/FIS - Flight information region/area/service
FPM - Feet per minute
GA - General aviation
GAAP - General Aviation aerodrome procedures
GFPT - General Flying progress test
GMT - Greenwich mean time
GS - Ground speed
IAS - Indicated airspeed
IFR - Instrument flight rules
ILS - Instrument landing system
IMC - Instrument meteorological conditions
ISA - International Standard atmosphere
kHz - Kilohertz
KIAS - Knots, indicated airspeed
KTAS - Knots, true airspeed
L/D -Lift/drag ratio
LAME - Licensed aircraft maintenance engineer
LMT - Local mean time
LSALT - Lowest safe altitude
MAP - Manifold absolute pressure
MBZ - Mandatory broadcast zone
MET - Meteorology
MP - Manifold pressure

Heading
Heading is the direction in which the longitudinal axis (or the nose) is pointed. It is usually expressed in a 3 figure number with reference to a particular datum. Heading is usually associated with magnetic north, however in some instances it may be required or considered useful to select an alternate datum.

Bearing and track
Bearing and track are measured identically the same to heading. While heading is where the nose is pointing, track is the direction in degrees the aircraft is actually travelling. Bearing is the direction to and from a feature or a navigational aid.

Runway numbers
Runway number is based on the actual direction of the runway (in a 3 figure heading) minus the last figure of the 3. It is simply rounded to the nearest 10 degrees.

Relative Positioning
Relative Positioning, with reference to the pilot sitting in the cockpit is often expressed as the 'o clock code'. It is a standard communication where the ability to use exact (3 figure) heading readouts is impossible or impractical. To picture it easily, sit an analogue clock in your lap with the 12 facing up. Use can include traffic avoidance, aerodrome sighting, or simply an easy way to point out a landmark or feature.

Distance, Speed and velocity
- The unit for distance for en route navigation is the nautical mile. It is equivalent to 1,852 meters or 6,000 feet.
-The unit for speed is the knot. One knot being one nautical mile per hour
-Wind velocity is described in terms of the speed in knots.
-Wind direction is described in terms of from what direction the wind is coming from.

Vertical distance
The unit for vertical distance is the foot, which is approximately one-third of a meter. There are specific meanings for terms regarding vertical distance, as sometimes the datum from which height is measured is not the same.
-Altitude is the vertical distance above mean sea level (or MSL) . For MSL to be accurate the pressure setting must be set to either the local QNH or the internationally standard 1013Hp above the transition level.
-Elevation is the vertical distance of an aerodrome or landmark above MSL
-Height is the vertical distance above the ground. Either above aerodrome level (AAL) or above ground level (AGL) depending on the reference

[NOTE] AMSL is always used to show the elevation of objects in aeronautical maps.

Universal time
The time reference used in aviation is the universal time constant (UTC). The time is also known as Greenwich mean time (GMT) or Zulu (Z) time. The reference is the actual time at the royal observatory in Greenwhich, greater London, or the 'zero meridian' .

Local time
Local time is the time on your watch or the TV news. It is the UTC time adjusted for the time zone you are in.

Flight times
-Airborne time is the time from takeoff to touchdown. Also called, flight switch or air switch
-Chock to chock is the term usually used to describe the time from engine startup to engine shutdown. It serves two purposes. The total engine running time as to comply to maintainance schedules, and the number in which a pilot enters into his/her logbook.

Fuel/oil Volume
The almost standard international unit for fuel is the liter. To my knowledge only the US continue to use the 'gallon'. 1 'USG' is approx 3.8 liters. The standard oil measurment is the US 'quart', which is equal to one quarter of a standard US gallon as the name suggests.

In some cases it is required to convert the volume of a liquid to weight. To convert the volume of a liquid to weight you need to know the specific gravity of the liquid. For example AVGAS has a specific gravity of 0.71. i.e. one liter weighs 0.71 KG.

Conversion factors
Through out a person's life they will no doubt stumble across the need of conversion once. Although at home a simple Google search will convert any number, when you are in the air the internet is not so readily available. The following rules of thumb are valuable knowledge to hold.

Celsius to Fahrenheit - Multiply by 1.8 and add 32
Centimeters to inches - Multiply by 0.394
Feet to meters - Multiply by 0.305
Fahrenheit to Celsius - Subtract 32 and multiply by 0.556
Horse power to kilowatts - Multiply by 0.7458
Imperial gallons to US gallons - Multiply by 1.200
Imperial gallons to liters - Multiply by 4.546
Inches to centimeters - Multiply by 2.540
Kilograms to pounds - Multiply by 2.205
Kilometers to nautical mile - Multiply by 0.539
Kilometers to statute miles - Multiply by 0.621
Kilo pascals to pound per square inch - Multiply by 0.145
liters to imperial gallons - Multiply by 0.220
liters to US gallons - Multiply by 0.264
meters to feet - Multiply by 3.281
meters to yards - Multiply by 1.094
pounds to kilograms - Multiply by 0.454
pounds per square inch to kilo pascals - Multiply by 6.895
nautical miles to kilometers - Multiply by 1.853
nautical miles to meters - Multiply by 1853
nautical miles to statute miles - Multiply by 1.151
statute miles to kilometers - Multiply by 1.609
statute miles to nautical miles - Multiply by 0.868
US gallons to imperial gallons - Multiply by 0.833
US gallons to liters - Multiply by 3.79
Yards to meters - Multiply by 0.914

Mental calculation
If you don't have a calculator oin you some of the conversion factors above can be quite hard or impossible to calculate mentally. Bellow is some mental conversion rules of thumb that should allow you to process a convertion mentally...

Millimeters to inches - Multiply by 4 and devide by 100
Meters to feet- Multiply by 3 and add 10% of the result
Kilograms to pounds- Multiply by 2 and add 10% of the result
Celsius to Fahrenheit- Double it and subtract 30 for temperatures below 20 degrees C, double it and add 25 for temperatures above 20 degrees C
Fahrenheit to Celsius-Subtract 30 and half for temperatures below 70 degrees F, Subtract 25 and half for temperatures above 70 degrees F

Ball park figures
It is always best to do a rough mental check to keep your calculations honest...

-1 USG is roughly 4 liters
-1 liter of AVGAS is roughly 3/4 KG
-i USG of AVGAS weighs roughly 3KG
-1 nm is roughly 2km
-60 knots is roughly 100ft per second

Specific Gravities
To work out the weight of a liquid volum you need to know the specific gravity of the volume. You simply multiply the volume by the specific gravity to find your answer.
-Water= 1.0 (I liter of water is 1KG)
-AVGAS= 0.71 (1 liter of AVGAS is 0.71KG
-AVTUR= 0.8
-Oil= 0.89




More to be added....

Very helpful... cheers Eric.

Thanks for putting that together Eric. The topic is now pinned.

Would these be "Rules of thumbs"?

When flying into differing pressure areas the following will help remember how your altimeter will be affected...
"High to low, look out below! Low to High, clear blue sky."
The altimeter will read a higher altitude than actual when flying into lower pressure area, putting you closer to the ground than you see on the altimeter. Look out below! The opposite is also true.

When seeing another aircraft's nav lights the following tells you how he is oriented to you...
"Red on right, fearful sight."
means red light on right and green on left means he's heading straight for you.

For VASI approach slope lights,
"Red over white you're all right, red over red you're dead."
Self explanatory.

I got some rules of thumb
1. To see more ground, push forward
2. To see more sky, pull back

Add 2% airspeed for every 1000 ft altitude flown to find TAS

Decrease .02% in airspeed when flying through haze.

Distance required for descent = 3 x Height in Thousands of feet.
Litres to Kilos = multiply by 0.8
Crosswind, remember three numbers, 0.5, 0.7 & 0.9 for 30, 45 and 60 degrees of crosswind. Multiply these by the windspeed to get crosswind component.
Airspeed (in mine) reduces at 1.5kts per second.
Rate of descent in fpm on 3 degree glideslope = G/S x .5 (150 kts = 750 fpm)

I'll sure I'll remember some more soon!

PM

All good stuff!! Stick yer thumb on yer map (Aeronautical Chart, for the f-arts down at the CAA) measure along the Nautical Mile scale the distance from your knuckle to the end of your thumb - depending on how big your thumb is the distance will be.....whatever. Then when you are in the air and busy, you can just place (the inside of, bent) your thumb on the chart (see map) and measure your distances to somewhere. How far to your next point, or to your destination..? lay down your thumb and measure it. Da-daaaa! Rule of Thumb.
================================================================
Mach 0.75 = 7.5 NM / minute, (still air, not ground speed, still handy though) Try it out1 Divide 411kts by 60 and see what you get.... now work out the Machno..... see, its about the same - only TAS though.
===================================================================
Rule 573, Don`t f-art around with the wind in a fast jet doing Mach2.0
=================================================================
Guage during a flight, what 2 NM and 5 NM looks like from the flightdeck at 2,000 5,000 feet.
Same for jets, 20nm 50 10000 20000
================================================================
Wanna stay in control of your nav? Time. Time your legs in minutes. Look for your waypoint when the leg minutes are up and don`t be false to it. Make each route at least with a `half way point`
================================================================
Offtrack but finally know where you are - lucky you, that is an achievment - so how to get back on track or continue direct to Destination - its the one in 60 rule!!
Say you find yourself 5 miles to the right of track and you work out that you have been flying for 10 miles, obviously, you wanna get back on track or direct to destination - right? Then its the one in 60 rule.
Quick calc - in your head - distance off x 60 divided by dist gone. So five miles offx60=300? Happy?
Divide by the 10 miles gone = 30 So, you must alter heading by 30 deg, what will that do? That will make you parallel track.
Any good to you / NNNNNOOO!! So, then you do the whole thing again dist off x 60 div by DIST TO GO now say you have 20 miles to run then dist offx60/dist to go = 30 deg (again because you are still off track) div by 20 = 1.5 degrees. Now you add the two totals together and you get 31.5 degrees. frightened? You should be, try this one, Just double the track error and you will be back on track in the same amount of time it took you to get off it.
Dist off x 60/dist gone So, in our example - 5x60=300/10=30 now double this 30 track error = 60 now alter your heading (towards your track (!)) by 60 degrees [note how long it took you to get in this mess from takeoff] = xminutes
so in xminutes time you will be back on track - promise. Look on your chart, to find out what you will see when you get there, a river, a road, a railroad track, a farm spread, an industrial zone, a forest? and aim to see that in xmins time.
===============================================================================
Here`s a Gotcha! You are flying on a heading of 230 deg mag with a groundspeed of 100kts VAR 5 degs. having applied 15 degrees of Left drift due to the wind, when you were flight planning. Suddenly, you decide you want to turn back, for whatever reason. Do you do a 180? Nope (because you may not get there unless it is very close) Therefore, you have to calculate your new heading by applying the drift differently as - you are going the other way and the wind will be affecting you differently. So, set yourself up in the class room at your flight school/club and buy the instructor a coffee and figure out how to do this. Hey, your Groundspeed will be different too and so therefore will be your time.
================================================================================
===
If the ground rises up gradually below you (increasing high ground) you can be sure the cloud above you wont be !
================================================================================
===
Flying up the side of a mountain...? Fly at right angles to the mountain i.e., not straight up it - that way, if you get an engine failure, you simply turn the nose towards the lower ground 90 degrees(downwards). same if you are daft enough to stall, edge the recovery towards the downslope -( without using your ailerons of course.) ask your instructor about this.
================================================================================
====
Them great hills and mountains. Fancy going over the small mountains on a lovely day? - watch out for turb, yes, turb coming off the mountains, it will cause you to bang your head on the ceiling of your `lil plane and it will also make you jump.
Read up on Standing mountain Waves and rotors too and associated turb. The turb can hit suddenly like a punch.

Don`t be tempted to fly over the top and descend down a wide gully that is in the SHADE. This although good fun screaming down a narrow valley - if in the shade, the cooler heavier denser air WILL be racing DOWN the valley and, Near to the bottom, when you decide to pull up, you will pitch up but still keep going downwards! This is due to the cooler and heavy denser air racing down to the bottom of the valley drawn down by the reduction in pressure at the bottom due to the rising less dense hot air over the hot plains. If you hit the hot plains before you hit the ground you may get away with it - I did. Actually, I increased my rate of climb by applying full power and setting up the climbing attitude but the climb rate was marginal compared to when I went back into the sunshine over the hot wheat fields. Kept me talking all afternoon back at base.
================================================================================
======
Got your instrument? Great, if you pick up ice and you are....anywhere, tell ATC this is especially effective if on the approach. They will give you instant feedback - like ``descend to 1500ft`` or whatever.
================================================================================
=====
Also, If your rate of Descent is half of your groundspeed then why start down early for a tail wind or late for a headwind? As, the RoD is to be the same as the half the G/S then whatever the G/S is, is going to be the factor in the RoD so starting down later or earlier aint valid -- re: post of--- just before Christmas titled ...Descent.
================================================================================
====

Wann get a fast reciprocal on your heading? I.e., wanna turn 180? Easy - plus 200 - 20

So, 238 - 200 + 20 = 058 and 260 - 200 + 20 = 080 and 240 -200 + 20 = 060

090 + 200 - 20 = 270 . . . .easy peasy. 360 - 200 + 20 = 180 " awww - its a doddle ! "

===================================================

To find out the Mach Num for where you are . . . find your Outside Temp. (OAT)

To find your OAT look on the OAT guage !! or calc your flightlevel say, 250 x 2 + 15 = temp.

FL250 = -50+15=-35

273-35= sq rt it, then x 38.94 = your Machno

edited 25/02/09

Also, if I may, for the Specific Gravity don`t forget folks....``Weight to Volume Divide`` which means when you are in the exam and you need to calculate 13,000 kg and give the answer in litres (I nearly said metres!) then DIVIDE by the specific gravity (s.g.) So, take a typical s.g. of 0.8 then your 13,000kg becomes. . . ? how many litres. . . ?. . . hmmm? If you look, you can find it all on your whizz wheel/pocket computer (which every pilot will probably have) or just use your calculator (if allowed in your particular exam).

? this made post in error

To remember weather to add or subtract the magnetic variation remember
"West is best" Therefor, add the west variation, and do the opposite to the east,-subtract.

You goddit in one baby!

therefore 245 + Var 7 W gives what . . . ? (+plus)
and 005 - Var 7 E gives what . . .? (-minus)