Helicopter avionics ... a pilot's guide to instrument flying

The sphere of flying by helicopter instruments is growing rapidly. With the introduction of better icing clearances and more sophisticated helicopter avionics, procedural instrument flying has now become a reality.

For your helicopter pilot training, simulation of instrument flying conditions will be achieved by blanking off any window areas on your side of the helicopter and you wearing a visor to further restrict your peripheral vision.

It is important that you learn to relax during instrument flying. Before flight, make sure that the seat and pedals are adjusted to give you maximum comfort. Remember that the basic techniques for instrument flying are exactly the same as for visual flight.

Constant practice is required to achieve a regular and efficient scan, together with gentle control movements.

The concept of the selective radial scan centres around the Artificial Horizon (AH), then to a second instrument, back to the AH, on to a third instrument, back to the AH and so on.

When carrying out any particular manoeuvre the scan should concentrate on the instruments relevant to that manoeuvre .

It is wasted effort to include helicopter instruments which, at that stage of the flight, provide no useful information. For example, in a level turn the scan would follow the sequence - AH-VSI-AH-ASI-AHCOMPASS-AH-VSI etc.

Note that the altimeter is not included in the scan since the VSI will give the first indication of a change in height. Should a change in height be detected then the altimeter must enter the scan sequence.

ATTITUDE CONTROL

During your initial helicopter flying training, emphasis was placed on attitude flying. If a correction was required, the helicopter's attitude was adjusted against the visual horizon. When you fly on instruments the real horizon is no longer available and so the Artificial Horizon (AH) must be used instead. No basic change in technique is required; you simply use the AH in the same way that you see the real horizon in visual flight. Thus it is the primary instrument for selecting and determining the helicopter's attitude - the master flight instrument.

The pitch datum on the AH can be adjusted to be coincident with the horizon bar for any flight condition. Remember that any small attitude change shown on the AH will, if maintained, have a marked effect on the helicopter and therefore it is usual to set the datum against the central mark on the side scale and leave it there throughout the flight.

To avoid large attitude changes you must be extremely smooth on the cyclic and any changes must be small. Remember too that there is a lag in helicopter response so be patient and allow time for it to stabilize before making any further changes.

Helicopter instruments 

THE INSTRUMENT TAKE-OFF AND CLIMB

Your instructor will hover, taxy and position the helicopter for the instrument take-off because of the restricted visibility from your side.

The initial part of the instrument take-off is carried out visually. In the hover carry out normal hover checks and when ready initiate a 'towering type take-off'. Ensure the 'wings' are level, maintain compass heading and check balance. Confirm that the instrument indications agree with the visual facts and transfer to instrument flight by 100 feet agl.

Maintain the accelerative attitude and anticipate the attitude change to establish the best rate of climb speed for your particular helicopter. Adjust power, check balance and use bank if necessary to correct heading.

During the transition and climb, the scan should follow between AH-ASI-AH-COMPASS-AH-BALANCE etc. Power should be included as necessary. The altimeter will assume greater importance as you approach your required height but apart from confirmation of serviceability, can be excluded in the early stages of the transition.

When levelling out from the climb, anticipate the height as normal and use the APT technique. If the helicopter is slightly off heading, check balance before applying any bank.

LEVEL FLIGHT AND SPEED CHANGES

Your instructor will show you level flight indications throughout the IF flight envelope for your type of helicopter. The important point to notice is that the speed stable attitude varies very little throughout the range.

The AH is used to select and maintain the attitude. The other instruments are used to monitor and confirm the helicopter's performance and are therefore referred to as PERFORMANCE instruments.

In level flight at a steady airspeed, the speed table attitude should be maintained. Initially, deviations from level flight will be indicated by the VSI; the altimeter in the helicopter suffers from large lag errors and takes some time to respond to height changes.

If a rate of climb or descent is indicated refer to the AH, then the ASI. Make an appropriate small cyclic adjustment to correct the attitude, allow the helicopter to settle and then recheck. If a climb or descent is still indicated but airspeed is stable, adjust power and maintain balance.