On approach into MEL on Friday (VA B737) the guys up front were constantly applying and reducing thrust. I've not normally seen this. The approaches normally are fairly smooth and constant. There was also a bit of turbulence too as we descended (we tracked in from SYD over what appeared to be Eildon and other areas north of Melbourne). Would that have affected the aircraft's speed?
For much of the duration of a flight, we aren't all that concerned about slight speed deviations. But, the closer you get to the ground, the more important it becomes to be exactly on speed. The aircraft has to be flown down a very narrow line, which will give us the correct track to the centre of the runway, and a constant 3º descent angle. Sadly, the conditions (wind, thermals) conspire to push us off our desired line as well as giving too much, and too little, airspeed.
If you are too fast, you'll need a lower pitch attitude, and higher sink rate to stay in the slot. You'll also tend to fly high out of the slot, which then has a nasty habit of leading to late corrections, and landings without sufficient power and falling through the flare into a solid (and likely shortish) landing. Slow will often lead to low, and the correction for that tends to make you float. It's very dynamic.
So, the best answer is to keep on top of the corrections. Don't let the speed deviate. Hang on to the slot. The aim is to get to the end of the approach with the aircraft in the right spot, power at the right level, speed on target...and that will lead you into a normal flare. If the conditions are gusty, you can end up 'throttle bashing' with constant changes of power. All changes in an aircraft are multi stage. If you find yourself going slow, you need to increase the power enough to get you back to the target. When you get there the power will then have to be reduced to hold the speed. Each power change will also give you a pitch couple, so that will have to be corrected simultaneously.
