STABLE APPROACHES
landings that have been completed despite the aircraft being unstable on approach. On certified aircraft the Aircraft Flight Manual (AFM) is usually well constructed, clearly describing the configuration options together with recommended approach speeds. However, chatting with pilots who have had such bad experiences, without exception they have all selected an approach speed at, or above, the highest speed quoted in the manual. Many pilots on approach add a few knots for luck, not realising that these extra knots actually contribute towards them having to rely on luck. Sure, there are times where extra speed may help (gusty conditions) but, generally speaking, an aircraft should be flown within the speed range described in the AFM. Importantly if there is a speed range quoted, the top end of this range applies to an aircraft at maximum weight, whereas ‘lighter’ aircraft should be flown towards the bottom end of this range. Once the desired speed is obtained pilots should trim to it and minimise the amount of control input necessary to maintain a stable approach.
Excessive speed (energy) brings all sorts of problems during landing. First, any landing distance performance calculations can be dismissed but, as importantly,
the aircraft is going to spend more time losing energy in the flare before finally touching-down. During this extended time period, there is scope for the wind to create mischief and the pilot to relax back- pressure on the control column to try to expedite the landing. It’s this last action that leads to bounced nosewheel landings, prop strikes and bent firewalls. My first top tip is to ensure that the aircraft is trimmed at an appropriate approach speed.
RATE OF DESCENT AND POWER While it’s relatively easy to adjust the rate of descent in a light aircraft, some pilots forget to address the secondary effects of doing so. Whether rate of descent is actually controlled by power or pitch might be a common after-flying bar discussion, the reality is that adjustment of either requires a corresponding input from the other. Think of it like this: Power + Pitch = Performance (P+P=P). So, if a pilot chooses to fly an approach with an excessive rate of descent, he or she needs to carefully plan energy management when finally reducing this rate of descent in order to achieve the required performance.
A low rate of descent or ‘shallow’ approach can also bring problems. It’s
A stable approach - nailed
likely that the engine will be developing significant power while the aircraft is being ‘dragged in’, followed by a tendency to cut or ‘chop’ the power over the runway threshold to complete the landing. At this point a ‘stable’ aircraft has just become unstable; the P+P=P equation has changed, slipstream effect over the empennage has reduced and there is a likelihood that increased control column back pressure is required due to the aircraft being out of trim.
Piece of advice number two – plan and set a reasonable rate of descent. In most GA aircraft, this is around 500-750ft/min.
AIRCRAFT CONFIGURATION This element largely relates to flap settings and ensuring the wheels are down (which is good). Again, the key element is setting-up the aircraft early enough that you do not need to reconfigure at the latter stages of the approach. Adding flap changes the performance of the wing so you have to adjust pitch and/or power to maintain the desired performance. That said, for many GA aircraft the application of the last stage of flap merely reduces speed by a few knots and this can be used as part of the approach planning. However, it's not advisable for pilots to significantly adjust flap settings at low
Nose, prop and wing damage is most common
SPRING 2021 CLUED UP 15
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