Alternate law L/G question.

[Bobpudge]

They said in alternate law, once you put L/G down, the aircraft goes to Direct law.

However, in the FCOM (DSC-27-20-20-20-A), it states that ALT 1 flare mode is the same as normal law's flare mode.

Flare mode starts at less than 100 ft RA and flare mode is essentially a direct stick-to-elevator relationship with some damping provided by the load factor and pitch rate feedbacks and below 50 ft RA a slight down pitch order is applied automatically (according to FCOM). Pitch up inputs will execute the flare.

Im now confused. Is it correct that upon putting landing gears down, from alternate you go to direct law meaning there will be no flare mode (losing the pitch down order below 50ft RA)? Then why would alternate law have a flare mode? :ugh:

It is not stated on the FCOM if direct law has its own flare mode. Can't find any clarifications. Will appreciate any help and clarifications thanks.

PS. Will be doing my simulator session next month but trying my best to understand everything about the plane (a330) with the help of the FCOM. Sorry for a beginner question.

Thanks :)

[giggitygiggity]

Possibly it does indeed have a flare mode, as I understand, the new sharklet A320s coming out of Airbus stay in Alternate Law when you put the gear down (after whatever failure) so there will have to be some sort of flare mode attached to that. I assume it would be complicated for a normal sim to replicate this but I would be interested to try it out.

[vilas]

Bobpudge
"it is not stated on the FCOM if direct law has its own flare mode. Can't find any clarifications."
Direct Law makes the Airbus like a conventional aircraft. Does conventional aircraft need flare mode? In fact going in direct law is the flare mode of alternate law.

[Bobpudge]

Hello Giggity, that will make a lot of sense, the plane staying in alternate law even at gear down.

Hello Vilas, true direct law makes it fly like a conventional aircraft but flare mode is not entirely just direct law. As i understand it, flare mode is a mode where in there a direct stick-to-elevator relationship AND it also provides an autmatic nose pitch down during the fell with the intention to give the pilots a "feel" on the controls when executing the flare.

Direct law alone will not provide that automatic nose pitch down. (Not clarified in the FCOM). But this is a different question.

What I really want to know is:

Will alternate mode upon landing gears down change to direct law? Meaning there will be no flare mode (no auto pitch down but still have that direct direct stick to elevator relationship)?

Or

Will it not change to direct law and just continue with its flare mode (as stated in the FCOM)

I think the main confusion for me was when I read it on previous thread the alt law goes to direct law upon landing gear down (which i haven't read in the FCOM)

As of now i think alt law will just remain in alt law even upon gear down since it was never mentioned in the FCOM:)

[Chris Scott]

Hello Bobpudge,

It would have been helpful to your readers if you had told us - preferably in your title - which model of Airbus you were referring to, instead of burying it (a330) towards the end of your opening post. This seems to be a common and quite unnecessary omission by OPs. :ugh: So don't take this complaint personally!

The A320s I flew were early models, with a RAT that was susceptible to stalling with the L/G down and the a/c in sideslip. Now, guys - what happens on the newer Airbuses, including recent models of the A320 family? Has the A320 RAT position/design been adjusted to enable use of RAT for electrics with the L/G down? If so, has this enabled any changes to the flight-control laws for the landing?

[vilas]

Bobpudge and Chris Bob you have misunderstood the purpose of flare mode. Imagine landing without flare mode, as you flare, as long as the stick is out of neutral aircraft will continue to pitch up with auto trim catching up so you will have to neutralize the stick and start again and again.This pumping of the stick is not a good way to land and will not produce consistently good landings. Therefore in normal law flare mode is introduced to make the aircraft pitch down from 30 feet so that pilot can continue to maintain backward pressure on the stick as required. Also auto trimming is stopped. This mode is not possible in alternate Law (at least in A320)so the other way of doing this is to put the aircraft in direct law where during flare with closing of thrust and with dropping speed nose keeps dropping and pilot can keep pulling on the stick and land in conventional way. In other words in alternate Law flare mode begins at gear down in form of direct Law. In alternate law if you put the aircraft in unusual attitude aircraft goes in abnormal attitude law which does not revert to direct law with gear down and it is not easy to land the aircraft in alternate law without flare mode. Chris, as you can see this has nothing to do with the RAT. On all later air crafts the RAT is functional even after gear down till after touchdown.Quoted below from FCOM FLARE MODE In pitch alternate law the flight mode changes to the flare mode when the pilot selects landing gear down. The flare mode is a direct stick-to-elevator relationship. (Refer to DSC-27-20-20 Direct Law)

[Chris Scott]

Hi vilas,

That's a very good explanation of flare mode. IIRC, it was only conceived as a result of the early flight testing of the A320, for the very reasons that you have stated.

Thanks also for pointing out that the reversion from pitch-alternate law to a stick-to-elevator mode at L/G extension on the post-certification A320 was not, as I had thought, to cater for the loss of the RAT-powered emergency generator. I am correcting my post. You are quite right to imply that the flare in a load-factor law would be very strange to the pilot, who would be accustomed to the flare mode of Normal Law. So a stick-to-elevator mode is the better option.

My reason for thinking that pre-certification A320s (prior to the reconfiguration of the electrical system) retained pitch-alternate law to touchdown was that my August 1987 (pre-certification) FCOM makes no mention of the downgrade to pitch-direct law at L/G extension. That may or may not have been an error of omission by the technical writer. A later FCOM, dated 17 Feb 1988 (about the time of A320 certification) amends the Pitch Alternate paragraphs as follows:
"In pitch alternate law the flight mode changes to the landing mode [sic]at the selection of L/G down or at the selection of Flaps 3 [sic]. The landing mode is a direct stick-to-elevator relationship."
[READERS NOTE: THE ABOVE QUOTE IS OUT OF DATE.]

As you can see, the terminology and descriptions of A320 FBW were still evolving when I was on my tech conversion course and simulator in Jan/Feb 1988. As for the present, I do not have access to the DSC-27-20-20 reference that you suggest.

[sierra_mike]

the new sharklet A320s coming out of Airbus stay in Alternate Law when you put the gear down (after whatever failure)

having access to fcoms of A320 with sharklets, i found no information about that. i looked over some abnormal procedures (on the sharklet aircraft) which lead to alternate law and they also have the line "WHEN L/G DN: DIRECT LAW" in it.

[giggitygiggity]

You are completely correct, I was mistaken. I remember reading over something briefly in a presentation and didn't take it in fully. What it actually said was 'In case of yaw damper loss, when the landing gear is extended, the yaw damper remains in alternate law (previously switched to direct law)'. Again, this was taken from a presentation rather than the FCOM. I am yet to fly a sharklet A320.

Apologies for confusing the issue further.

[sierra_mike]

just looked over the procedure for yaw damper system loss on a sharklet a320 and you are right giggitygiggity. you will stay in alternate law after gear down on a sharklet a320 while you go to direct law after gear extension on a "classic" one. interesting

[vilas]

Sierra mike
That means normal flare mode is available for landing with yaw damper loss just like Alt1 in 330. Can you check on that please?
giggity, It is only with yaw damper loss the flight controls will change to alternate law and remain in alternate law with gear down.

[Bobpudge]

Hi vilas, thanks for the info. You said:

"Therefore in normal law flare mode is introduced to make the aircraft pitch down from 30 feet so that pilot can continue to maintain backward pressure on the stick as required. Also auto trimming is stopped. This mode is not possible in alternate Law (at least in A320)so the other way of doing this is to put the aircraft in direct law."

But A330 FCOM says ALternate mode has a flare mode. Now I do not know what to believe. :ugh: i will just have to check on with my instructor during our sim session. Maybe A330s are different from the 320s with regards to this topic. Will post here of any information/clarification i will get.

Thanks for your insights guys. :)

[vilas]

Bob
A330 alternate1 will have flare mode as in normal law.a320 didn't have it. Now with sharklet for yaw damper failure it seems they have introduced it.

[sierra_mike]

That means normal flare mode is available for landing with yaw damper loss just like Alt1 in 330. Can you check on that please?

at least the line "WHEN L/G DN: DIRECT LAW" is missing in the status info for a yaw damper system loss on the sharklet version while it is mentioned in the status info for the "classic" ones
(Ref: FCOM/PRO/ABN/ABN 22-Auto Flight/AUTO FLT YAW DAMPER SYS)

[Bobpudge]

Thanks Vilas, you made it more clear now. :D I will keep on reading the FCOM and keep on learning. thanks again for everyone's time. Safe skies.