How to Fly Helicopters

Preparing For Flight

We all go out to our helicopter and complete our daily preflight inspection before flying. But what exactly does the preflight consist of? Is it just a matter of checking the mechanics of the helicopter? Of course this is a very important check but there are many more things to check and consider.

• Licence expiry date
• Medical expiry date
• LPC renewal date
• Aircraft documentation
• Location of helicopter
• Fuel
• Mass and balance
• Meteorological reports
• Fitness for flight
• Passenger brief
• Dangerous goods
• Airport layout and procedures
• Planning, ATC and route
• Performance
• Equipment
• Prior permission to land at destination

Some of the above items may seem obvious to you but I bet that you do not check all of them. I may even have missed a few. But let’s look at these in a little more detail.

Licence expiry date

Were you aware that your JAR licence has an expiry date? Take it out and have a look at it. It is not obvious but normally, on the second or third page, there will be an expiry date. Put this date in your calendar and set an alarm to remind you to renew it – no one else is going to do this for you. There will be no letters to remind you.

Your licence is only valid for five years. This is separate from your type rating.

Obviously you must not fly if it has expired.

Medical expiry date

Check the expiry date of your medical. Do you have to wear corrective lenses? Do you have a second pair as stated on your medical certificate?

Again, program the expiry date into your calender with an alarm to remind you to renew it before it expires.

LPC renewal date

Check the date when your LPC is due for renewal for the type of aircraft you are flying. Use the calender again.

Aircraft documentation

Make sure the aircraft is airworthy. Check the following documents:

• Certificate of Registration (CoR) (no expiry date).
• Certificate of Airworthiness (CoA). This is being replaced by an Airworthiness Review Certificate
• Certificate of Release to Service (CRS). Check that the helicopter has not exceeded the hours and dates for required maintenance.
• Airworthiness Review Certificate (ARC). This is an ongoing, continuous airworthiness program certificate.

Helicopter Engines

One of the most common helicopter engines used today is the turboshaft engine. A turboshaft engine is effectively a jet engine and normally runs on a kerosene based fuel. There are many variants of turboshaft engines but they all follow basic concepts and principles. To keep things simple, I will be referring to the engine used by the Bell 206 JetRanger. The Rolls Royce Allison 250/c20J.

The working cycle of the turbine engine is similar to that of the piston engine. There is induction, compression, combustion and exhaust. The major difference is that unlike the piston engine, the turbine engines cycles are continuous. Unlike airplane jet engines where the exhaust gases provide the thrust, the exhaust gases for the helicopter turbo shaft engine are intercepted by a turbine that transfers the energy from these gases to a gearbox that provides power for the helicopter.

It is vital that you learn not to over-torque or over-temp the engine as this can have disastrous consequences for someone flying it, weeks or even months later. Misusing the engine will not necessarily cause a problem right away.

Starting the helicopter engine causes more stress to the components than just about any other operation due to thermal shock and wear. For this reason, the start cycles are counted and recorded in the technical log after each flight. As helicopters tend to fly for short periods compared to airplanes, it is possible that the engine could reach its start count limit before it reaches its useful life hour limit. Start-ups are expensive and so it is better to leave the engine running for ten minutes while waiting for a passenger rather than shutting the engine down and then starting up again.

The engine relies totally on the battery or Auxiliary Power Unit (APU)  for startup. The engine has to be turning fast enough to keep enough cold air flowing through the turbine otherwise it will become very hot and damage the internal components. A weak battery could run out of power before the combustion process becomes self sustaining and this would be disastrous.

A “Hung Start” can happen if the engine fails to accelerate and the RPM stays constantly low. This uses up your battery power and if the battery runs out of power then the engine slows down, less and less cold air is drawn through the engine and subsequently the temperature in the combustion chamber becomes really hot within a few seconds causing a lot of damage.

A “Wet Start” is the equivalent of a flooded engine and the igniter has failed to light the fuel. Wait for at least 5 minutes and then vent the engine. Because the battery has already been partially drained by the failed start and the venting, it is probably a good idea to get an external start using an APU to make sure you do not run out of power on your next start attempt.

If you follow the check list exactly then you should have no problem starting the helicopter engine every time. The most common reason I have seen for hot starts is low time pilots starting the engine with the throttle already partially (or fully) open.

Therefore it is vital for you to double check that the throttle is fully closed before pressing the starter button.

Turbine engines take time to “Spool up” or “Spool down” when you make power changes. For this reason you should operate the collective or throttle very smoothly to prevent engine “surging”. Surging can happen when the airflow over the compressor blades becomes disturbed causing them to stall. This leads to loud banging noises (similar to a shotgun going off) and a very noticeable vibration from the engine. Shut down immediately if this happens during startup.

The Air Inlet

The air inlet is designed to stabilize the air before it enters the compressor. A particle separator may be fitted at this point to remove any foreign matter such as dust or sand which could cause erosion of the compressor blades.

The Compressor

What is Fog?

We all know that fog keeps us on the ground when we want to be flying. But are you aware that there are different kinds of fog? Do you know the conditions that are required for fog to form? Do you know about radiation fog, advection fog, frontal fog, sea fog and hill fog?

This post should refresh your memory or perhaps even enlighten you.

Mist and fog occur when tiny water droplets are suspended in the air causing a reduction in visibility. Mist is very similar to fog and differs only by definition:

When the visibility is less than 1000m – FOG exists. Relative Humidity = 100%.

When there is reduced visibility but visibility is greater than 1000m – MIST exists. Relative humidity < 100%.

Water droplets come into existance due to condensation which causes the water vapour in the air to condense out as a liquid. This normally occurs when the air is cooled by an underlying cold surface or by the interaction of two air masses.

Different Types of Fog

There are three different types of fog and they form under specific conditions:

1. Radiation fog
2. Advection fog
3. Frontal fog

Radiation Fog

The conditions required for the formation of radiation fog are:

• Moist air – (high relative humidity) that only requires a small amount of cooling to reach its dewpoint temperature.

Pronouncing Numbers

During a recent flight I was cleared by ATC to climb to “fifteen hundred” feet. If you are an aviator, you should be aware that the number “fifteen” is never used in standard radiotelephony. I decided to make this post to let you know how to transmit numbers  when using the radio.

Transmission of numbers is frequently done incorrectly and this post should make you confident in how to do it.

Transmission of Numbers

Numeral                Pronunciation

0                              Zero                              Bold Text shows correct pronounciation

1                               One

2                               Two

3                               Tree

4                               Four

5                               Fife

6                               Six

7                               Seven

8                               Eight

9                              

Different Types of Tail Rotor Failure

While training for a JAR PPL(H) licence, you will be told about tail rotor failures. There is no flight exercise for tail rotor failures under the JAR system however I like to demonstrate the different types of tail rotor failure that can occur during flight. They are as follows:

• Tail rotor failure in the hover
• Tail rotor failure in forward flight
• Stuck left pedal
• Stuck right pedal

Although tail rotor failures are extremely rare, I have been unfortunate enough to have experienced one. Because of my training, I was able to identify it and land safely. If you have a sufficiently large, flat area, there is no reason why you should not be able to do the same should this ever happen to you.

Some books that cover this topic are:

Tail Rotor Failure in the Hover

When the tail rotor fails while hovering, the nose of the helicopter will yaw rapidly to the right (in helicopters that have a rotor that turns anti-clockwise when viewed from above). You will automatically apply more and more left pedal to try and compensate but this will have no effect and you will eventually reach a point where you have full left pedal applied but the helicopter is still yawing to the right. You should now have realised that the tail rotor is not working.

You must immediately roll off the throttle and perform an engine off landing from the hover. By rolling off the throttle, you will have eliminated the torque and the helicopter will stop yawing immediately. Keep the helicopter level and let it settle. Just before the skids touch the ground, start raising the collective to reduce the rate of descent.