Tuesday, 26 August 2008

PPL Ex 13: Normal Circuit, Approach & Landing Ex 13

The numbers are based on a Cessna 152: Practise your Straight and Level lessons when flying the downwind leg. Look out and fly with reference to the visual horizon. Again the principle of Lookout - Attitude - Instruments should be applied. LOOKOUT and using the visual horizon is most important. As far as possible, keep the power constant at 2150RPM (possibly tighten the throttle friction a little more) and make small elevator and aileron inputs to remain straight and level at 1000ft AAL. There is another good mnemonic (or do I mean acronym?) to consider when pressuring the controls: C.C.H.A.T. which stands for Change - Check - Hold - Adjust - Trim. It means that should you need to change the ATTITUDE or the POWER, then make a small change, check (i.e. stop the movement), hold the change and look at the instruments, adjust if required, and finally trim. At 2150RPM the IAS should be approximately 90KIAS and there should be little or no rudder input required to balance the aircraft.
Keep a very good lookout AND listen out for other aircraft. By listening to other traffic and to ATC you can build a picture of what is going on in the airport vicinity and who is where.
Call downwind when abeam upwind end of the runway and do the pre-landing checks. These are normally BUMFFICHH: Brakes OFF Undercarriage DOWN (Fixed!) Mixture RICH Fuel ON and Sufficient for Go-around and DIVERSION Flaps AS REQUIRED Instruments Ts and Ps CHECKED and Altimeter SET Carb Heat CHECKED and set as required Hatches SECURE Harnesses SECURE and FASTENED. (Note: The Brakes should always be off in flight. The Undercarriage is 'welded' down. The Mixture is always rich below 3000ft. The Fuel should be ON else we would have had to make a forced landing somewhere, and if we are short of fuel where better to be than in the circuit? There is no ELECTRIC FUEL PUMP on a Cessna 152. Flaps should still be at Zero. Instruments are routinely checked. Why would the Hatches and Harnesses be anything but secure and fastened? For my money the important checks here are: Mixture RICH. Altimeter SET. Carb Heat CHECKED and always scan the Ts and Ps).
The wind direction and strength is ALWAYS important to the pilot who should develop an awareness of what effect the moving air mass is having on the aircraft. In an ideal world in order to land with as low a ground speed as possible the runway for landing is always that closest to into wind. Of course we do not live in an ideal world and other factors have, also, to be considered by ATC or the Authority with regards to the runway for landing. Some of these other factors could be obstacles in the approach or in the go-around path, length, slope, noise- abatement etc.
Before turning onto Base Leg have an idea of what the wind effect will be on Base Leg. Will there be a HEAD WIND COMPONENT or a TAIL WIND COMPONENT?
If there is a HEAD WIND COMPONENT then consider delaying power reduction AND to a higher power setting than the standard 1500RPM datum when you do judge it necessary , and if there is a TAIL WIND COMPONENT consider early power reduction to, possibly, a lower power setting than the standard 1500RPM datum.
Select Carb Heat ON and DECREASE POWER to the datum plus an increment or minus a decrement as stated above. The nose of the aircraft will want to drop with the decreased power. Do not let it! It is very important to maintain the height(QFE)/altitude(QNH) as power is reduced. Progressively increase the attitude as the aircraft decelerates in order to maintain the altitude. Include the ASI in your scan, and when the IAS is inside the WHITE ARC (Flap limit speed) and, depending on the HWC, select Flap 20 (pausing briefly at Flap 10 because all selections made in an aircraft are 'considered', 'measured' and 'deliberate'). It is important to stress: maintain the height/altitude as the speed reduces. The speed deceleration now 'increases', due to increased drag, and as the aircraft approaches 65KIAS start the descent at the appropriate 'glide slope angle'. The fixed pitch propeller will also mean that the RPM will have decreased, so re-adjust the power as required.
Line up with the runway centre-line and note the wind direction by observing the windsock. Apply the appropriate amount of drift to maintain the aircraft on the centre-line all the way down the approach path.
Now that the aircraft is lined up with the runway, the speed should be reduced to 60KIAS (+ 1/2 of the headwind component - HWC). E.g. if the wind is 260/12 and the runway is 23 (say 230-deg Magnetic) then the wind is 30-degrees off the runway heading and from the right. 30-degrees off = .866 of 12 = 10 and 1/2 of 10 = 5. So add 5kts to 60 = 65KIAS. See Tip in next paragraph.....
(Tip: How to quickly figure HWC: 10-degrees off centre-line = 98% of Wind. 20-degrees off centre-line = 94%, 30-degrees off = 87%, 40-degrees off = 77%, 50-degrees off = 64%, 60-degrees off = 50%, 70-degrees off = 34%, 80-degrees off = 17% and of course 90-degrees off = 0%. BUT let's be practical about this:
0 & 10 = 100%. 20 & 30 = 90%. 40 = 80%. 50 = 60%. 60 = 50%. 70 = 30%. 80 = 20%. 90 = 0%.) Thinks: maybe I will eventually put all the 'Tips' in one separate place - when I get time!
Fly the approach at 60KIAS +/- the HWC and use the Throttle and the Control Wheel to control the GLIDE PATH (or the "approach path" if you prefer) and the IAS. To state that you conrol the 'Glide Path' with the throttle and the 'speed' with the elevator is over-simplifying the operation. If you are high and the speed is correct then you must decrease the power. If you are low and the speed is correct then you must add power. If you are fast and on the glide path then you will have to co-ordinate elevator and throttle movement (power reduction) in order to reduce speed and stay on the correct glide path. If you are slow and on the glide path then you will have to co-ordinate elevator and throttle (power increase) in order to stay on the correct glide path. Start to develop an awareness of the 'energy' of the aircraft.
Flying the approach requires constant concentration and judgement. The questions that you should be mentally asking yourself all the time are: Am I high? Am I low? Am I fast? Am I slow? Am I left? Am I right?
In order to mentally answer these questions it is very important to keep changing the focus of your eyes (extensions of the brain!) to the runway (the DATUM) and the ASI. Look OUT, look IN, look OUT, look IN. look OUT, look IN.......................so that we are making judgements all the time with reference to the 'picture' of the runway and the IAS. There are various schools of thought about exactly where to 'look' when looking OUT. My strong advice is to look at the far end of the runway. Your peripheral vision will take care of the big picture, including obstacles in the approach, the touchdown zone and, later, the flare (or roundout) and the de-crab. Attitude flying, as stated elsewhere is of paramount importance, and the approach and flare is no exception. This is the only way to ensure a successful and safe landing every time.
Okay, we are still flying the approach.....
If the HWC is strong, then you would consider delaying selecting FLAP 30 (Landing Flap) until later in the approach. Do not add drag when more power is needed to fly the approach. If there is little or no HWC, then consider earlier selection of FLAP 30 (Landing Flap). Calm conditions can be tricky on a short runway and we will need to get the aircraft stabilised with Landing Flap at the correct speed and on the glide path in good time.
It might be a good idea to call 'Final' with the selection of Landing Flap, but remember that 'Final' is inside 4nm of the runway threshold and where you call 'Final' may depend on what is going on in the circuit.
Having selected
Flap 30, the extra drag will 'bite' and the IAS will decrease with no change in power. Now fly the aircraft at 54KIAS
+ 1/2 HWC. You may need to add a smidgen of power and there may be an attitude change, and therefore a small trim change.
As the threshold of the runway is approached, keep the 'crab' angle on and, if the IAS was correct as you cross the threshold, close the throttle but do not allow the nose to drop. Control the attitude of the aircraft and concentrate on still looking at the far end of the runway. Do not dive for the runway. Peripheral vision will dictate to your brain where the ground is and where the touchdown zone is, and as you close with the runway surface, still looking as far down the runway as you can, gently pressure back on the control wheel to 'arrest the rate of descent'. It is worth stating AGAIN: Do not dive for the runway. The final part of the approach should be a continuation of the glide path. Just before touchdown push (we never "kick" the rudder!) the rudder to align the aircraft with the centre-line and touchdown. This may cause some roll due to yawing the aircraft, but this is easily controlled with aileron. Keep straight using rudder. Hold the nosewheel off the ground and use aerodynamic braking until you are about to run out of elevator authority. Now gently lower the nosewheel onto the runway and keep straight. If braking IS necessary lift your feet up to the brakes and gently apply symmetrical braking. Do not lock the wheels.
Keep aware of what is going on and do not delay vacating the runway. When clear of the runway perform the after landing scan.

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