Sign in to follow this  
Guest groundpounder75

747 descent

Recommended Posts

Can any 747 expert inform me if it is normal practice to slow a 747in descent with the speed brakes/spoilers. I am using Meljet 747`sand all do not slow even with only 1000 set as the descent. Therefore,I have to use the spoilers to slow effectively. The situation getsbetter once flaps are deployed.Any help would be appreciatedYoursJohn

Share this post


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

No not always. I recently flew on a SIA 744 (9V-SMU) in real life KJFK-EDDF and no spoilers were used during descent. You should be able to descend at 2000ft/min with idle thrust without gaining speed and without spoilers. Spoilers are used for expedited descent (e.g. up to 3000ft/min). The Meljet airfile has some serious issues. Not slowing down properly and being overpowered are some of them. But hey, you can't really blame the guy, after all he's a one man show and it's freeware. His principal talents are clearly in the model building area. Misha

Share this post


Link to post
Share on other sites

As indicated in an earlier thread by a real life pilot, a pilot would normally reduce speed of his aircraft and would normally use a common sense of judegment to use speed brakes to reduce to a certain speed if need be, Hence, doing so until ATC instructs him to a slower speed.Note: Common judgment to reduce speed is based upon the point of descent and distance away from the airport. Pilots needs to reach a restricted altitude given to him by ATC and reach this point within reasonable distance/speed away from airport...Troy

Share this post


Link to post
Share on other sites

While not a real life "Heavy" pilot, my friend is a retired Northwest 747 captain. He says he never used the speed breaks except for landing. He decended rather rapidly to 10,000 or other assigned altitude according to the approach charts, then let the speed blead off before decending lower.

Share this post


Link to post
Share on other sites

John,The response here is based on flying the 747-100/200 aircraft over a 7 year period. The -400 should not be SIGNIFICANTLY different.Standard descent practice in the classic was to descend at idle power starting out holding Mach .84 then flying 320 knots to 10,000 feet.Vertical speed would vary during the descent between 2500 and 2000 fpm typically, depending on groundspeed. My personal practice for descent planning was to first check the aircraft weight at top of descent. Near max landing weight (630,000 lbs), I would allow altitude x 3 + 10 miles for the descent ( i.e. FL350 x 3=105 miles + 10= 115 miles). At weights approaching 450,000 lbs or less, I would drop the extra 10 miles off the end of the formula. (105 miles in the above example instead of 115)The descent would be managed so as to be level at 10,000 feet and slowed to 250 knots by 30 miles out from the airport. Usually this required 7-10 miles room to slow the aircraft to 250 from 320 at 10,000 feet.... NO AIRBRAKES USED.An alternate method is to reduce speed from 320-250knots by shallowing the descent to 1000 feet per minute when descending out of 12,000 feet, which usually produced the desired 250 knots by arrival at 10,000 feet.Except for some increase in distance or decrease based on headwind tailwind situations, the above procedures were very reliable.Airbrakes are only used in the 747 when ATC throws you a curve ball and asks for a tight crossing restriction late in the descent profile, requiring a "tightening" of the descent profile. At least all the COMPETANT 747 drivers I worked with did the same! (smile)Best Regards,Tim Sanders

Share this post


Link to post
Share on other sites

Try Flight Level Change. The plane will descend at the speed set in the speed window on the MCP. The plane will pitch up or down to maintain this speed. The drawback is that you may not descend as quickly as you would like. I just flew on a Delta MD-11 from Atlanta to Orlando this past Monday and I think our cruising altitude was FL390 or FL370, I can't remember which, and that flight is only one hour. Well, when we started our initial descent we came down hard and fast. I have flown a ton and I have never felt a descent like that before. It was pretty wild.

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