Cabin Altitude alert

[grid777]

why sometimes when flying at FL430 there were cabin altitude alert
but sometimes it was alright

Is it relate with pressure around there or not ?
How can i know that there would be cabin altitude?

Notice: B777

I am flying PSS777 (Flight Simulator)

please advice me

regards

[enicalyth]

It is impossible to say what has gone wrong but from a Boeing course I attended in 1998 buffet onset is, say, lift coefft = 0.69

If you were heavier than about 241600kg then you maybe had no business to be at FL430 M0.84 and the sim quite rightly stung you though its warning signs seem a bit odd. However FL390 should be fine. Try that.

I hope that makes some sense. Have a look at the documentation they supplied and keep within the flight envelope. If you poke the bear eventually the bear pokes back.

Keep up your interest in simming but do remember your pastime is only based on as much data as they can sell for $50 and make a profit. So most of it is eye candy, certainly not approved by the maker and can therefore teach you bad habits.

All I can say is read your manual and stick to it and in this case a better forum might be for simmers. But nice to meet you and good luck.

[NSEU]

Unfortunately, Boeing (or whoever) rarely give out enough information in their manuals to properly model pressurisation systems (even if the programmer wanted to spend a lot of effort on this system).

In manuals, there are typical flight profiles, but they don't cover all scenarios.

Did you have VNAV engaged? Did you have both packs running? What was your landing altitude? What was the differential pressure when you got the cabin warning? Write as much information down as you can think of.. then email the sim designer. Perhaps he/she can help you.

Rgds.
NSEU

[ad-astra]

So let me get this right.

A genuine (if not a somewhat obscure) question was asked and two members CHOSE to reply with what I thought were fairly dignified replies.

The next 5 members GO OUT OF THEIR WAY to express their disbelief that their time has been wasted reading such a post.

Move on without venting your superior attitude!

Well done gentlemen! :=

[john_tullamarine]

What ad-astra said ....

This forum is for tech queries. Whether such enquiries originate from a B777 25,000 hour veteran, an RC enthusiast, or a simmer is irrelevant, I would have thought.

Providing the question is relevant to aviation and the discussion is reasonably polite then, unless the hierarchy dictates otherwise, the question is fine and should be addressed in a professional manner.

I have no problem with folk holding a view one way or the other but let us consider the possibility that the original poster may be a simmer now .. but might end up at the other end of the spectrum if we provide a bit of encouragement.

It would be very sad if we let Tech Log become unaccessible to other than an annointed few.

[Old Fella]

Being one of those labelled as having a "superior attitude" and having had my post removed I would simply ask "What is the question actually asking"?

Flight at FL430 is given and it is stated "there were cabin altitude alert but sometimes it was alright". "Is it relate to pressure around there or not"? "How can I know that there would be cabin altitude"?

Not knowing anything about the B777 I am unsure of what triggers a cabin altitude alert, however I would assume that a differential pressure which allows the cabin altitude to reach 10000' would. Why do we have insufficient differential? Well, any number of reasons relating to either air supply or flow control, be it pack flow in or conditioned air flow out, cabin pressure control problems. As for the last part of the question I am unsure of what is being asked, however I guess it relates to an indication of actual cabin altitude on a cabin altitude altimeter.

The Tech Log should not be made inaccessible to any legitimate questioner Mr Moderator, but it does loose some relevance with questions worded in such a way as the one which started this thread.

[john_tullamarine]

The Tech Log should not be made inaccessible to any legitimate questioner Mr Moderator, but it does loose some relevance with questions worded in such a way as the one which started this thread.

Agreed. Regardless of what a mod might do, some will find it wrong .. goes with the territory. My position regarding awkward or poorly posed questions is that the forum folk are in a good position to play with the original question and eventually tease out what the original poster was trying to ask. In the process I suspect that others on the sidelines will learn a bit along the way ?

I see my role quite clearly as not being the arbiter of what is sensibly rigorous or trivial but, rather, to keep the lunatic fringe at bay (rarely a problem in Tech Log) and to keep the discussion on a reasonably even keel.

When next I am driving north past Taree (probably later this month) perhaps we should have an ale and discuss matters philosophical ...

[muduckace]

What is up with all the caustic hostility here?

Sounds like your sim is generating a genine warning. In real life with most commercial aircraft they are designed to operate at a max differential pressure of less than 9 psi creating a cabin altitude of about 8k feet above sea level. The cabin altuide alert I know of in most aircraft goes off at a cabin altitude of 10.5K feet.

Basically you are operating your simulated aircraft above the specified altitude to provide a safe berathing environment for your sim pax.

[SOPS]

I am not smart enough to work out differential pressure maths..but I can tell you two things 1. The Cabin Altitude Alert in the 777 goes off at 8500 feet cabin alt and ,2 last week I flew for 7 hours at FL430 in the 777 and we never got a Cabin Alert...I must admit I never looked at what the actual cabin altitude was.