Approach and Landing airspeed techniques

[Centaurus]

A question which has puzzled me for years. I learned to fly in the RAAF in the early 1950's. In those days most military Pilots Notes stated approach and landing speeds as over the fence figures. We were taught to land by using gradually reducing airspeeds from the time base leg was commenced until arriving over the fence at the Pilots Notes recommended airspeed. It was commonly known as the bleeding back airspeed technique. The fighter "buzz and break" was an example of this technique where relatively high airspeed was used on what was termed "the initial" and airspeed bled back in a tight low level circuit. The theory was a wartime technique to have enough energy before touch down to counter an enemy intruder attack.

Since the introduction of jet transports the approach and landing technique has changed to a fixed airspeed approach depending on the weight and flap setting. For example, the so called stable approach criteria where the VREF plus wind additive is established by mid final and held until the flare. The difference between the two techniques being the former uses a steadily bleeding airspeed to arrive at the manufacturers recommended VREF at the threshold versus a fixed airspeed technique established early on final.

It could be argued the bleeding airspeed technique requires finer judgement of flight path and airspeed control while the fixed airspeed is easier for (say) a coupled approach.
Maybe the difference between the two airspeed techniques is something to do with jet transport swept wing handling characteristics? Discussion appreciated.

[Tu.114]

At what IAS was the "bleeding airspeed" procedure started?

Basically, if I do not misunderstand the procedure, it would remove the 1000´ stabilisation gate and replace it with the same at about 50´, thereby slightly speeding up an individual approach.

Not having operated this procedure, I´d assume that returning to or reassuming this procedure would require a solution to the following questions:

- What influence does it have on airport capacity and ATC? A steady flow of aircraft at constant, controller-given speeds would appear much easier to handle and to allow much more traffic per time than allowing every aircraft to bleed off its airspeed as it sees fit.

- How about engine spoolup time and go-arounds? A stabilized approach flown at a steady speed and with spooled-up engines will usually allow for much quicker engine reaction than (essentially) a glide approach with engines at or near idle all the time.

- How are different speeds between types catered for? An airport that sees a steady flow of traffic ranging from say ATRs to the odd A380 will have to solve the issue of very different speed reduction profiles with (usually) the turboprop able to keep up speed the longest. A military airfield that has only fast jets of comparable performance or even of only one type operating will likely be only marginally affected by this.

In total, this procedure would seem to bring individual aircraft down an approach in a marginally shorter time at the price of a noticeably reduced airport capacity. So it is a minimal gain for a few but a loss overall...

[yoko1]

Different techniques for different aircraft and different arenas of operations.

In the arena of modern commercial transport aircraft, the answer is basically the technique mandated by your employer, which as you stated is the stabilized approach criteria that has been pretty much adopted worldwide. The reasons that the airlines have converged on this criteria are many, but it is the currently accepted best practice.

[Capt Scribble]

Swept wing military aircraft are very high drag in the landing config and it is easy to loose speed over the fence if you are a bit fast. They also tend to be able to stop quickly on military runways which are normally quite long. Today's airliners are slippery little beasts and it has been judged that the decision as to whether you have got everything under control for landing will be made generally at 1000ft (other criteria are available). This takes away the option for the pilot to hope for the best and, it will be ok, when the approach is too fast or high. Being stable at 1000ft also allows for factors such as positive wing shear to be coped with more easily on finals. Oh, and the military chap has his rapid exit facility if he goes off the end.

[CanadianAirbusPilot]

At my airline we have two stabalization gates.

At 1000 feet we should have the aircraft configuration selected (if flaps are still in transit its okay) with a reasonable assumption you will be fully stable at the second gate.

At 500 feet we need to be on profile, configured, on speed -5/+10 (unless temporary wind conditions exist and are corrected) with the thrust usually above idle.

I feel its a good alternative to the 1000 foot hard gate used many places.

We are apparently looking at changing to having a 200 foot stable gate vice 500 foot gate with the intention that from 500-200 feet the PM will constantly note the unstabalized condition. The hope here is to have a higher compliance of go arounds if you hit the gate unstabalized so you're not having crews intentionally non-comply if say you're at 500 feet at 15 kts fast on a 12,000 foot runway and countinuing. You absolutely should be stable by 500 feet, but gives you some discretion with a hard floor.

Apparently were about average for go arounds compared to the industry and they want to see it go higher. Making the stabalized gate lower I suppose makes it a harder gate.