Sign in to follow this  
rivermivida

Loosing speed at FL350! Mayday!

Recommended Posts

HiPlease, check the attached pic. I was flying at cruise alt, and suddenly started to loose power and speed. The FMC says buffet alert.I don´t know what´s going on!!Thanks!2j4ws3o.jpg

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Who let Jimmy Buffet in the cockpit.... And get his hand off the throttle!^ Bad joke.I never get a buffet alert, I want one too! ;)JB

Share this post


Link to post
Share on other sites

You might be too heavy to safely fly at FL350, or it could be too warm, or too strong of winds. Check the FMC CRZ page and see if you're above max altitude. Seeing as VNAV isn't engaged, that could be the case.

Share this post


Link to post
Share on other sites
You might be too heavy to safely fly at FL350, or it could be too warm, or too strong of winds. Check the FMC CRZ page and see if you're above max altitude. Seeing as VNAV isn't engaged, that could be the case.
i went to FL300....looks stabilized now...73 kt at FL350 are heavy winds?Thanks

Share this post


Link to post
Share on other sites

I had this exact problem yesterday. Were you perhaps using ActiveSky? I was, and the winds at FL350 were 100KTS and would move 180 degrees from headwind to tailwind. That would cause a -100KT airspeed change, causing speed to drop below 200 and buffeting. I changed ActiveSky to DWC and used some settings I found from a search on these forums. Flew the same route and it was perfect! So, I would check whatever you are using for winds. I am sure it is the culprit.

Share this post


Link to post
Share on other sites

Yeah, it could either be your airplane is too heavy, or ActiveSky. It's done that to me several times, and is really frustrating.

Share this post


Link to post
Share on other sites

If you have a registered version of FSUIPC, you can tell it to filter the winds to no more than so many degrees or knots per second for change. That really helps.My first thought was that you're too heavy for the altitude, but I can't be sure without knowing your weight. It's a more common problem than you think, though, as most simmers don't know the first thing about aircraft and fuel loads.

Share this post


Link to post
Share on other sites
Maybe your pitot tubes froze due to supercooled water-ice and this made you lose the speeds or IAS DISAGREE? Did you accidentally fly into a bad storm?
That only happens theoritically on scarebus's over the Atlantic Ocean between Brazil and Paris.

Share this post


Link to post
Share on other sites
Maybe your pitot tubes froze due to supercooled water-ice and this made you lose the speeds or IAS DISAGREE? Did you accidentally fly into a bad storm?
No bad storm at all. Maybe it was the weight: 120 pax and 99% fuel. (doing a 6 hours flight)
If you have a registered version of FSUIPC, you can tell it to filter the winds to no more than so many degrees or knots per second for change. That really helps.My first thought was that you're too heavy for the altitude, but I can't be sure without knowing your weight. It's a more common problem than you think, though, as most simmers don't know the first thing about aircraft and fuel loads.
Maybe it was the weight: 120 pax and 99% fuel. (doing a 6 hours flight)
I had this exact problem yesterday. Were you perhaps using ActiveSky? I was, and the winds at FL350 were 100KTS and would move 180 degrees from headwind to tailwind. That would cause a -100KT airspeed change, causing speed to drop below 200 and buffeting.I changed ActiveSky to DWC and used some settings I found from a search on these forums. Flew the same route and it was perfect!So, I would check whatever you are using for winds. I am sure it is the culprit.
Yes, i use AS, but what is DWS...?
That only happens theoritically on scarebus's over the Atlantic Ocean between Brazil and Paris.
And it will be more...remember this is the last year for humanity. (we´ll not see the PMDG 777...that´s sad)

Share this post


Link to post
Share on other sites

Yeah, FL350 is pushing it for 99% fuel. I believe there's a weight/altitude table in the manuals, but they're on my other computer. Look at the CRZ page. It'll tell you exactly what your MAX ALT is. Chances are, you were over it.

Share this post


Link to post
Share on other sites

THE FMS will ya in INT REF if what you put in is too high! I want a BUFFET ALERT never had that one

Share this post


Link to post
Share on other sites

Yeah, with 120 pax and 99% fuel, I'd say its definitely the weight. For a 6 hour flight, you can simply do step climbs to get to a higher altitude along the way. I'd say an initial cruise with 120 pax and 99% fuel is FL300-FL330.

Share this post


Link to post
Share on other sites

I had a similar experience some time ago. At CRZ and got BUFFER ALERT displayed on the CDU. Then everything started to go crazy, VNAV and LNAZ disengaged, instruments went haywire, warnings and alerts everywhere (I know I'm not describing this very well). Anyway I realised I had no duct pressure and was getting oxygen warning lights. It then occured to me that I had forgotten to set the CRZ ALT for cabin pressurisation so it had remained at 10,000. Well I won't make that mistake again. This actually happened in real life with Helios Airways HYC 522, 14th August 2005 (my respects for any family or friends of the victims who may be reading this). I believe this was caused because the cabin pressuration valve was left in the manual position after routine maintanance.

Share this post


Link to post
Share on other sites
I had a similar experience some time ago. At CRZ and got BUFFER ALERT displayed on the CDU. Then everything started to go crazy, VNAV and LNAZ disengaged, instruments went haywire, warnings and alerts everywhere (I know I'm not describing this very well). Anyway I realised I had no duct pressure and was getting oxygen warning lights. It then occured to me that I had forgotten to set the CRZ ALT for cabin pressurisation so it had remained at 10,000. Well I won't make that mistake again. This actually happened in real life with Helios Airways HYC 522, 14th August 2005 (my respects for any family or friends of the victims who may be reading this). I believe this was caused because the cabin pressuration valve was left in the manual position after routine maintanance.
Edit: I may in fact have left a door open but can't recall.

Share this post


Link to post
Share on other sites
I was flying at cruise alt, and suddenly started to loose power and speed
You wouldn't SUDDENLY lose airspeed if it had been caused by being too heavy!!! You have both engines operating (so you haven't lost POWER) and your RAT seems not too high so the most probable culprit is WINDSHEAR - sudden change in windspeed or direction. Since the wind is showing as being a crosswind in your jpg it may have been a strong headwind and suddenly shifted to that crosswind. That would certainly explain the sudden slow to buffet speed. If using STANDARD ASE (or AS2012) it helps to also have Dawson's FSUIPC and set wind change settings to 5 seconds / degree. That would force FSX to change wind direction or speed more gradually. Also, as has been suggested, you can use the DWC option in ASE/AS2012 and that will control FSX sudden shifts. Imagine if that sudden WINDSHEAR occurred right after takeoff or on short final! It can and does occur in RW and can be a killer if not dealt with immediately and properly. Edited by HiFly

Share this post


Link to post
Share on other sites

This Happened to me.. I was struggling for a good 20 mins to why i was slowly losing airspeed. I was flicking through the COMMS manual, trying different altitudes.... Nothing worked..... Then i realized my 2yr old daughter had lowered my landing gear........   :blush:

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this