Missed Approach Question (with video)

[frank marriott]

Engine cowl rash

 

 

[Roundsounds]

As FM states, an engine pod strike is of concern. Having said that Boeing aircraft use a wing down method on autolands, albeit with a lower crosswind limit than a manual landing - hence the differing techniques.

 

For further info' try typing the following into your favourite search engine:

 

- Airbus crosswind landing techniques

 

Although not officially a Boeing site, the following reference (copy and paste into a web browser URL field) reads like an extract from a Boeing Flight Crew Training Manual:

 

- flaps2approach.com/journal/2014/6/17/crosswind-landing-techniques-part-one-crab-and-sideslip

 

 

[dutchroll]

It appears the heavies set up in crab approach m in X winds. Any particular reason for not getting set up shooting straight the center line with x-control right from the start?

Fraught with complications in an Airbus.

The Airbus sidestick demands a "rate" from the flight control computers, not a flight control "position". So if you move the sidestick to the right to enter a cross-control situation, you are saying "give me xx degrees per second roll rate". Fifi then gets her abacus out and works out what flight control positions she needs to give you that roll rate and sends the corresponding orders to the flight controls. You can't fly down final approach holding the aircraft out of balance with a constant sidestick input, because you are then constantly telling it to roll to that direction at a particular rate, and that's what Fifi will give you - even if she needs full flight control surface deflection to do it.

 

In fact the whole system is designed to perfectly fly a crabbed approach. If you set the aircraft up tracking the extended centreline, wings level, and take your hands off the sidestick, it should (theoretically) stay wings level as it is attitude-stabilised in Normal Law and it should nicely track the runway centreline. In practice you do need very small corrective inputs though.

 

So the crabbed crosswind approach technique is always used.

 

In a Boeing, you can practically do it either way. However, historically pod scraping due to landing with excessive bank on has been an issue (though less so in later & larger Boeing models) so it has always been taught to fly the crabbed approach and kick it straight. Also it's more comfortable for the passengers, not making them think they're being thrown sideways out of their seats with crossed controls and a grossly out of balance condition all the way down final approach. Think what the out-of-balance situation would be like in 30-40 knots of crosswind!

 

 

[Marty_d]

Bloody Fifi, thinks she's so smart.

 

 

[facthunter]

A crab is an ordinary condition of balanced flight. You wouldn't know you were doing it if you didn't look outside. Your track made good is the runway centreline and your selected heading achieves it, if it's correct. Much as you do on a cross country but more exaggerated. because you are slower. (groundspeed) and your drift angle is more (usually)

 

Decrab is a rudder induced skidding heading change. Nev

 

 

[dutchroll]

....and another tidbit to add to Nev's comment above: flying a crabbed approach is standard airline practice, as explained above. To de-crab a Boeing or virtually any other plane, a smooth rudder input is made as the aircraft is flared, and an opposite aileron input is required to counteract the roll (secondary effect of rudder) and keep the wings level.

 

Not so with Fifi! The flight control laws do change on final approach, however roll remains "Normal Law", ie attitude stabilised if there is zero sidestick input. So to de-crab an Airbus you smoothly input the rudder to yaw it straight, but don't do anything with the roll. Well.....that's the theory. In practice Fifi takes a second or two to stabilise the attitude so you may need a blip of sidestick to get the wings level before the wheels touch. Not easy to do perfectly and not easy to do when you've been correcting for the secondary effect of rudder for your whole life!

 

 

[Tex]

Sounds lazy

 

 

[Guest Howard Hughes]

A crab is an ordinary condition of balanced flight. You wouldn't know you were doing it if you didn't look outside. Your track made good is the runway centreline and your selected heading achieves it, if it's correct. Much as you do on a cross country but more exaggerated. because you are slower. (groundspeed) and your drift angle is more (usually)Decrab is a rudder induced skidding heading change. Nev

Or you could just fly it on and let physics take are of the rest!

 

 

[ben87r]

That last one was insane!! Not going to try it tho!

 

 

[facthunter]

Probably near limit testing. If you do a hard contact (High ROD) with a lot of crab on there is a giant load on the undercarriage. Notice none of them allowed the upwind wing to get high. These aircraft have powerful ground spoilers that help keep the whole thing down, and the weight on the wheels. They are normally pre armed to extend automatically, as soon as a wheel turns. Without this feature there would be some very interesting situations in crosswind and skipped landings.

 

U/L's need the wing down near limiting conditions. Nev

 

 

[dutchroll]

Boeing flight test all their jets to max crosswind with no de-crab at touchdown. Not sure if Airbus do (I assume they probably would). This was always pointed out to us during crosswind landing training on the B767 as a "confidence" thing. It can be hard to get all the drift out before touchdown depending on the amount of crosswind component. The philosophy was always "if you suddenly realise you've undercooked it and will land with crab still on, don't panic, the plane will handle it just fine".

 

 

[Ryanm]

ATC wouldn't have offered 34 in normal circumstances. It would have been at the request of the crew, and for many reasons.

 

Going missed could have been due to becoming "unstable" during the final stages of the approach. Wind gusts can get you outside the stable zone very quickly.