A320 Minimum approach speed

[b.a. Baracus]

A quick question from a humble PPL:

On listening to the RT this morning, there was an aircraft cleared for immediate take off. Behind was a BA A320 which was told to fly minimum approach speed in order to give the departing aircraft a bit more slack. At this time the A320 was probably around 4 miles out.

Would the crew or FMC have not already worked out the optimum approach speed for their weight / configuration? If so would they have this minimum approach speed handy? i.e could they call it up on the FMC, or would it be a %age lower than original approach speed?

[tom775257]

Often we might fly something like 160 kts to 4 miles, so by saying reduce to minimum approach speed they are just saying come back to V approach. Many airports have the 160 to 4, so they might say this to you at 5 miles for example.

Another phrase used is 'reduce to minimum clean.' This would just mean the minimum maneuvering speed with no slat or flap. In the A32x and others this would be green dot speed, this is displayed as a green dot on our speed tape. This 'characteristic' speed varies with weight and altitude.

We wouldn't intentionally fly below the normal V approach.

Cheers.

[PappyJ]

Would the crew or FMC have not already worked out the optimum approach speed for their weight / configuration? If so would they have this minimum approach speed handy?

In the Airbus (All FBW Airbus), minimum speed is constantly updated and presented to the pilots on the PFD (Primary Flight Display, or the FMS (MCDU PERF Page)

With each change of configuration (Flaps) the information is again updated and displayed in Various forms in the same places. Clean = Green Dot, Slats = "S" speed, and Flaps = "F" speed, which are Minimum speeds for those configurations.

During approach, we have the same indications, plus Vapp (which may include a wind correction [GS Mini]) and Vls (The lowest selectable speed [albeit this one is commonly misunderstood by many pilots])

All these speeds are computed by the FMS (actually by the FAC's) and presented to the pilots for immediate reference.

I recall that the Boeing FMS performs very similarly.

I hope this sheds some light on it for you.

[Dan Winterland]

Most airliners will be flying a deccelerated approach. In otherwords. they will start the approach by intercepting the glideslope at a much higher speed that VAPP (V Approach). They typically intercept the glideslope with first or second stage flap selected, then will lower the gear then the remaining stages of flap aiming to be stabilised in the approach configuration at VAPP by 1000'(or whatever height their company ops manual specifies). This would be at 3.3 NM on a typical 3 degree glideslope.

If ATC want more or less spacing to get another aircraft off the runway or to maintain minumum separation for wake turbulence they will either ask them to keep a particuar speed until a certain DME, or in the case you heard, come back to VAPP earlier than 1000'.