Avoiding the Banana
Over the previous few articles I have discussed the landing and flare as a distinct event that happens over the threshold in the last 50 feet or so of flight. However, if you leave it until this point to think about your landing, well, it’s too late.
A good landing does not begin at the flare, rather it is set up early on final approach, allowing both the aeroplane and the pilot to relax and fly a stabilised approach all the way to the flare. Flying a large wide-body aircraft requires that I am stabilised at the final approach speed, at the correct configuration, on glide path and centreline by 1000 feet AGL.
What does this do for my final approach?
Firstly it gives me a point in space to aim for configuration, speed reductions and descent profile. Secondly, it gives the aircraft (and me!) time to get ready for the landing – allowing time for appreciation of the current weather conditions and traffic – as well as giving me a good feel for the aircraft in a trimmed out situation at the landing speed. Finally, and no less importantly, it prevents me continuing a rushed approach from where the aircraft may not be correctly or safely positioned or configured prior to landing. If I do find myself in this situation, i.e. not correctly configured or checklists not completed – I must carry out a missed approach, and give it another go – hopefully learning from the experience.
Another aspect of being nicely set up on final at a pre-determined point – be it height or distance – is that if at this point you are stabilised at your final approach speed, then changes to the aircraft’s power, and therefore attitude and trim, on late final will be minimised. This greatly reduces the pilot workload on final approach. How so?
Remember, the fundamental key to flying a stabilised approach is the relationship between attitude and power. On final – aircraft attitude controls aimpoint and power controls speed. This work cycle is slightly different to on base (to be discussed next month).
Another way to think of it is that whilst maintaining your target airspeed, the addition of power will make the glidepath shallower while reducing power results in a steeper glidepath. The net result is that if the aircraft is maintained at a constant speed (with constant power), the aimpoint will not change: easy if established already on your stabilised approach at the correct speed and profile. It is when either of these is off that we can find errors creep in, resulting in inaccurate glidepath maintenance.
For example, if your speed is initially high, power will need to be reduced to allow the airspeed to slow to the approach speed. If the attitude of the aircraft is not adjusted at this point (raised) to compensate for the reduced lift created as the speed reduces, then the rate of descent will increase, glidepath will steepen, and the aircraft will tend to undershoot. On recognising this, a pilot will then raise the attitude, reselect the aimpoint lower in the windscreen, and a shallower glide path will be the result. The end result is the aircraft flying a curved flight path to the runway – the ‘banana’ approach. To prevent this occurring, the pilot must understand the relationship between power, airspeed and aimpoint and that any changes to one necessitates an adjustment in the other.
To avoid the banana, recognise that decreasing airspeed requires increasing attitude and vice-versa. Think of it as a piece of string connecting the control column and the throttle/thrust lever running around your neck. Push the throttle forward, pull the control column back. Think about it, it does make sense. Get your instructor to show you the importance of aimpoint positioning in the window with differing attitudes. This is important – it can take some getting used to as it can initially seem the wrong way around. As your speed decreases, you must adjust your aimpoint down in the window – this does not shift the aimpoint up – merely adjusts the relationship to the window according to your line of sight out of the cockpit.
Getting yourself set up early on final is the key. This does not necessarily mean you must be as rigid as the airlines are about stabilised criteria, however, have a target position in your mind which is firstly achievable from your descent point, and secondly, allow enough time to relax and get in the groove for the landing. Understand the inter-relationships happening amongst speed, power and aimpoint. A stabilised aeroplane is a much easier machine to tame, especially if the wind is shifty or gusty, or you are at an unfamiliar field.