Temperature Conversion Rule of Thumb

This is not the best way to convert between Fahrenheit and Celsius! But it is the quickest, especially if you are doing the math in your head.

F = 2C + 30

This means that the temperature in Fahrenheit is equal to 2 times the degree in Celsius + 30. So if it is 10 degrees Celsius then 10 doubled is 20 and then 20 plus 30 is 50 Fahrenheit.

You can also convert the other way with the equation below.

C = (F – 30)/2

Warning! This is not exact at all.

The real equations are F = (9/5)C + 32 and C = (5/9)(F-32)

So if the AWOS gives you the temperature in Celsius and you just want to decide if you will need a sweater, then go ahead and use this rule of thumb.

If you need the information for calculating performance, then this rule of thumb is inappropriate to use and there is a much better way.


Instrument Flight Rules

Instrument Flight Rules, commonly called IFR, are a set of rules that apply to planes flying by instrument reference. This is in opposition to VFR (Visual Flight Rules), flown by visual references. Basically, if you can see where you are going, then VFR is an option, but IFR is always an option.

This set of rules requires a pilot to have an instrument flight plan and follow a set of procedures that govern communication and navigation.

IFR flying requires constant communication with ATC and a mixture of visual traffic separation when you are in VMC and reliance on ATC for separation when you are in IMC.

How do I know if I’m flying IFR?

If you have to ask, you’re not flying IFR!

But seriously, to fly IFR you will need to file an IFR flight plan, get a clearance from air traffic control, and comply with that clearance. You can fly IFR in VMC, but you can only log IFR, or “flight by reference to instruments” time when you are flying in actual IMC.

Flight Instruments: Directional Gyro

The directional gyro is a fairly simple instrument. It indicates the direction that the aircraft is heading. However, it does not sense the direction that the aircraft is heading.

How does the DG know which way the aircraft is heading?

The heading must be set in advance and the DG will keep track of whatever was set.

To keep track of the heading it uses a gyroscope. This method has some serious improvements over magnetic compasses, but a few drawbacks.

Source: FAA Pilot’s Handbook of Aeronautical Knowledge

The DG does not have the acceleration and turning issues that a compass has, so it is much easier to turn to a given heading without having to think about the lead and lag of the compass.

The presentation is just plain nicer and easier to read, but it also allows for more advanced add-ons like a heading bug all the way up to a full HSI.

For these reasons, you will be very hard-pressed to find a plane without a DG, even though a magnetic compass is sufficient to determine your heading.

When do I need to set my DG?

The DG needs to be set before takeoff and sometimes in flight.

Look at the knob in the image above. If you push that knob in and turn it, the whole card will rotate left or right as you turn. The tiny airplane image stays fixed in place as the headings turn under it. This knob is how the DG is set. Usually, this is done before taxi and then checked again after the runup.

In order to set it, we need to know the plane’s current heading. Luckily, on the ground a magnetic compass works pretty well so we simply read the magnetic compass and then turn the knob until that heading is set at the top of the instrument.

The instrument can be wrong for a number of reasons. Simply put, once the gyro spools down (when the plane is off), there is nothing to hold the compass card rigid in space. It tends to naturally be off by a few degrees every time you start up.

Imagine if you shut down with the DG pointing to 050 (like in the image above). Then you hook up the tow bar and move the plane into a tie-down spot facing the opposite direction. You have just turned the plane all the way around. What will happen to the DG? You will get in the plane and start-up facing 230, but the DG will still show 050.

Checking that the DG matches the compass is critical to removing these errors and being able to rely on the DG.

But there’s more. You will also need to set the DG in flight. Over time, due to internal friction, the gyro will precess out of place a little and the heading will be off by a few degrees. Personally, I set this using a mixture of procedures and situational awareness.

If I am on a cross-country, travelling somewhere, it is good to do this periodically as part of a cruise checklist (which you should be doing every so often during cruise).

As for situational awareness, there are times when the heading doesn’t seem to make perfect sense, or some reference point on the ground is 10+ degrees from where you thought it would be. This is a great time to check the DG and see that it matches the compass.

To set the DG in flight make sure that the wings are level and the plane is not accelerating (or slowing down). Then simply set it like you would on the ground. That’s all there is to it.

Accident Study: Landing Gear Failure

My local flight school had an unexpected incident recently involving a failure of the nosewheel. The plane was a Piper Arrow, which has a landing gear system that fails to the down and locked position. This means that if you lose hydraulic pressure, the gear will fall down and lock in position. It has an emergency extension system and even an automatic extension system if you forget.

The Piper Arrow is part of the Cherokee line of Piper aircraft. Over 32,000 of these popular planes have been built since 1961. The arrow itself is a very common plane and you might expect all of the problems to be ironed out. But this is aviation, and anything can happen, which is why we train so hard for what might happen.

In this case, the aircraft departed on a training flight with a very experienced student and a very experienced instructor. I know both of these people personally and have flown with them. They are some of the most qualified people anywhere to handle an emergency like this.

The gear won’t lock

The flight called for some stall practice, which involves flight in landing configuration, so the gear was lowered and raised several times.

However, the final time that the gear was raised there was a problem, although the pilots didn’t know it yet.

Upon returning to the traffic pattern the landing gear lever was lowered and the two main gear lights illuminated. The nose gear light did not illuminate! So they departed the pattern and tried raising and lowering the gear to no avail. They contacted the flight school and flew past so others could take a look.

The nosewheel was down, but not quite all the way, and it was off to the side a bit.

Luckily they had a good amount of fuel so there was time to think about how to handle this situation. The biggest question is about whether to land with the main wheels down or up.

A main wheels down landing would damage the nose of the aircraft if the gear collapsed, and the prospect of sliding in nose first was not very appealing.

However, landing with the gear up guaranteed damage to the plane and danger to the pilots even if the nosewheel was planning on staying extended. In addition, if the nosewheel did stay extended the landing would be very rough as the aircraft would necessarily roll to one side of the nosewheel.

They chose to land with the main wheels extended and locked.

Landing without a nosewheel

The landing was beautifully executed! The instructor touched down gently on the mains and kept the nose off the ground as the aircraft slowed. They pulled the mixture out so the engine would shut down just as the prop touched the ground.

The nosewheel slid partially up into the wheel well and the prop touched down with a loud metallic scraping noise. The plane settled onto the nose and slid down the runway. It appears that the brakes were not applied and the plane slowed down to a stop after a few hundred feet.


Some other instructors ran to the plane as the firetrucks rolled up behind them. There was no fire, and the damage to the plane was surprisingly minimal. The propeller is bent and the whole engine will need to be inspected and likely replaced, along with the motor mounts. The removable cowling is toast and the nose gear systems need to be rebuilt, but that is a very gentle outcome for the type of failure experienced.

What went wrong

This whole problem was caused by a small piece of metal that guides the nosewheel to a centered position as the gear is retracted. This guide ensures that if the wheel is down but turned slightly, it will be lined up to fit in the wheel well.

When the gear was raised after the last stall practice, the guide bent on one side and the roller that normally travels down the middle of the guide fell off to that side. Worse still, the bend in the guide rail was very sharp and it acted as a hook, grabbing the roller as the gear was extended! In the image below I am holding the bent guide. See the left side, which is how it is supposed to look, and the right side which has bent down into a hook!

IMPORTANT: Please read my disclaimer below about accident studies

This study and all accident studies are not meant to judge anyone, their actions, or their skills as a pilot. I do not claim to know what the pilot did or what he/she was thinking. The purpose of these accident studies is to better understand what causes accidents and how to avoid them. Comments and other points of view are always welcome as long as they are respectful towards everyone involved.

Instrument Meteorological Conditions

Instrument meteorological conditions (IMC) exist when an aircraft is in weather conditions that are not within the VFR visibility and cloud clearance requirements.

This means that you are in IMC if:
• You are inside of a cloud
• The visibility is too low
• You are too close to a cloud

When you are in IMC you need to be flying an instrument flight plan. Flying VFR into IMC is very dangerous and there are a multitude of accidents that occur this way. Don’t be a statistic! Stay away from the clouds.

In fact, I recommend having personal minimums for visibility and cloud clearance that are even more restrictive than the rules.

Visual Flight Rules

Visual Flight Rules, commonly called VFR, are a set of rules that apply to planes flying by visual reference. This is in opposition to IFR (Instrument Flight Rules), flown without visual references.

This set of rules allows a pilot to fly in most airspace without a flight plan, clearance, or ATC communication.

VFR flying requires constant vigilance for other traffic and reliance on oneself for navigation.

When you are flying VFR you must be in VMC.

Of course, while flying VFR you may choose to use air traffic control services to:

  • Get help in an emergency
  • Get directions
  • Get traffic advisories
  • Get clearance through airspace or to land

How do I know if I’m flying VFR?

Did you file and open an instrument flight plan? If not, then you are flying VFR. You must comply with all VFR regulations including visibility and cloud clearance minimums.

Visual Meteorological Conditions

Visual Meteorological Conditions, or VMC, are a set of weather conditions that allow for flying VFR.

Generally, VMC means good weather, but it also technically means that you are far enough between the clouds to allow for safe VFR flying.

For example, when flying IFR you might be popping in and out of clouds every few minutes.

If ATC notifies you about traffic then you must try to find the other plane. However, this only applies if you are in visual conditions at that moment. If you happen to be inside of a cloud you just respond with “IMC”.

In addition, it is also possible that you are near clouds and you can’t see the other plane because he is in a cloud. I will always take a quick look but if there is a chance that I can’t see the other plane because there is a large cloud right where he should be, I will still say “IMC”.

I am letting the controller know that the conditions where I am flying are not sufficient for VFR, even though I may be outside of a cloud at that time.

How do you know if you are in VMC?

I’ve devised a set of easy rules to help you remember the cloud clearance and visibility requirements for VMC.


Do you ever resent the FAA for making so many rules? This is an anti-authority attitude. It can be very hazardous because it can lead to poor decision making out of spite.

It’s ok to question the FAA about their many rules and feel free to even publicly denounce their many rules…..but only while on the ground. When you are in the air, you must fight against your anti-authority tendencies and remember this:

The rules are written in blood!

Most of the rules are there because somebody died doing something that was legal at the time. The rules don’t guarantee your safety but they do provide a framework of general safety limits.

Signs of an Anti-Authority Attitude

If you find yourself thinking some of the thoughts below (in bold) then you are experiencing anti-authority to some degree.

  • “Don’t tell me what to do.” The rules are usually telling you what to avoid, and while this may be inconvenient, there is a usually a pretty good reason. Follow the rule for now and find out why that rule exists after you land.
  • “This is a stupid rule.” It very well may be a stupid rule but professionalism and strict adherence to rules and procedures greatly enhance your survival chances.
  • “These rules don’t apply to me because I’m a better pilot than those who died.” Incorrect, you are a worse pilot than those who died in many ways. For example, you are letting yourself succumb to a hazardous anti-authority attitude. Those pilots who died before this rule existed were significantly more professional than you are being right now. Put down your pride and be safe.

Anti-authority goes hand-in-hand with invulnerability and is particularly dangerous because it leads to some of the most dangerous activities. Pilots who fly VFR into IMC or break up the plane doing unscheduled aerobatics usually suffer from both of these two delusions.

The rules and safety

Are the rules safe enough? No.

As pilots, we need to have personal minimums that are more restrictive than the rules. This is a personal decision and it will be different for everyone. For example, you only need 1 statute mile of visibility to fly in class G airspace, during the day, under 10,000 feet.

However, sticking to a higher minimum like 3 miles is probably a good idea.

Have you ever heard the phrase “8 hours bottle to throttle”? It means that you need to leave 8 hours time between drinking alcohol and flying. A better personal minimum that many use is “24 hours bottle to throttle”.

Be well aware of this attitude and decide in advance that you will be a professional pilot who follows the rules, even if you disagree with them.


Haze Layer

The air on our planet is full of particles of moisture. These are often visible as haze, usually in calm air or on humid days. Did you know that on many days, when the air is stable, you can get above the haze and the visibility goes way up?

Click on the picture below to view it full size. You can see the haze extending to the horizon and up to a clear “haze line”. Above this line the visibility is much higher. It will be easier to see other planes at this altitude.

Haze Layer – click to view full size

Calculating the top of the haze layer

The haze layer will generally be present in stable air where the temperature is above the dewpoint. At an altitude above the haze layer, the temperature will be below the dewpoint, so any moisture in the air will condense into droplets of mist of rain. Then gravity will pull these droplets down until they are back in the haze layer where they will turn back into water vapor (haze).

So the simplest way to find the top of the haze layer is to determine where the temperature and dewpoint will match.

The air is colder at altitude, but do you know how much colder? There is something called the adiabatic lapse rate, which is the rate at which the temperature drops as you climb.

It varies depending on the moisture of the air but as a rule of thumb just assume it is 2 degrees Celsius per 1000 feet of altitude. In dry air, it may be as high as 3 degrees Celsius.

So when you listen to the AWOS at sea level and it reports “temperature 12, dewpoint 6” then you can figure out the approximate top of the haze layer. That is a 6-degree difference, so we will need to climb 3000 feet.

This quick rule of thumb will let you make the haze layer calculation very quickly, just find the difference and divide it by 2 to get the altitude of the haze line.

for example:

Temperature: 10C, Dewpoint: 5C = Top of Haze Layer: 2500 feet

Temperature: 15C, Dewpoint 13C = Top of Haze Layer: 1000 feet

The next time you are flying start looking for the haze layer. It isn’t there every time, but it is there often enough (depending on where you fly).

Never Be 100% Sure

When I was a student pilot I had to fly a night cross-country flight with my instructor. I carefully planned the route and filled out my navlog. We took off in a Cessna 152 and proceeded to the destination, Carol County Airport in Maryland. About halfway through the flight, I was able to see the rotating beacon in the distance and I continued towards it.

I was 100% sure I had found my destination. I descended towards the airport and entered the pattern. As I landed I noticed that the runway number was wrong! This meant that the facility directory must not have been up to date. I taxied off the runway and then my instructor gave me the news. I had landed at York airport, in Pennsylvania. These two airports are 20 miles apart!

If I had not been 100% sure I would still have been evaluating the situation as I flew. That is why I will never tell you that I am more than 99% sure. This is a safeguard to ensure that I keep thinking and taking in new information to find the truth.

A huge 1% difference

My choice to be 100% sure meant that the new information (wrong runway number) was immediately treated as wrong! But if you take the 99% sure attitude, then you will treat new information as the truth and constantly reevaluate what you are seeing. If I had been 99% sure then I would not have put down my map and navlog. Instead, I would have seen rivers and cities and roads all in the wrong place and figured out where I really was.