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Guest Andrea

Engine power never IDLE during FMC descent to EBBR

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Hi PMDG team,before of all, many compliments to all of you for this 737 aircraft, the best I've ever flown in Flight Simulator.During a London Heathrow (EGLL) to Brussels (EBBR) FMC flight with cruise altitude at FL210 I noticed that the aircraft, from FL210 T/D to the ILS interception (EBBR runway 02 via ILS02 via KERKY transition via KOK STAR), has difficulties to loose height and speed because the engines remain at a minimum of 35.0 power (instead of IDLE I suppose), also after passing 10000 feet of altitude, where the aircraft (285 Knots of target descend speed in FMC) automatically switches off the VNAV light in MCP panel, switches on the LVL CHG and set MCP IAS at 250 as settled in FMC DES panel at SPD REST (250/10000). How can I help the aircraft to descend faster in order to arrive to the ILS interception fix with the right altitude (2000 feet) and the right speed (160 Knots) as suggested by the 02 ILS approach SimChart? Is it correct to press F1 on keyboard to reduce engine power? Take in mind that I set a 160/2000 speed/altitude constraint on the ILS interception fix point before taking off from EGLL airport and after speed reduction, passing the T/D fix, the altitude prediction of subsequent fixes was right.Questions:a) how 737 pilots really manage the descent phase?:( is it possible to reactivate VNAV after passing the 10000 feet speed restriction?c) why the 737 FMC, during descent, doesn't automatically reduce speed after passing STAR or TRANSITION fixes with speed restrictions?Andrea

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"(instead of IDLE I suppose), "this is actually flight idle, which is higher than ground idle, i'm not sure on the exact figure but 35.0 does sound alike it(i have a flight idle around 35.3).a) from what a friend of mine told me, they simply "play" with the speedbrakes and the power. :( Normally VNAV should not be disconnected after passing 10k or any other speed restrictionc) in my copy, it does do this right, it starts to reduce a bit before passing the restriction and mostly we are on schedule all the way.PS: the 160kt you mean for the ILS02 at EBBR is not a suggested speed but a MNM speed to be maintained untill the outer marker. In Brussels they are very strict about this, speed less than 160 and you'll be kicked(vectored) out of the stack...Cheers

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Many thanks Lenny, for your explanation about EBBR ILS approach.Regarding my question :( is it possible to reactivate VNAV after passing the 10000 feet speed restriction?" > I do not turn off the VNAV during descent, it seems that the FMC turns it off by itself after the first waypoint passed after T/D.Andrea

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and you do not get any message ala 'overspeed disconnect' in the CDU?

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a) Putting forcasted winds in the forcast page of the FMC will be a good start. A path can only be computed only if a mandatory "at" altitude restriction is on the Legs page (you will also see it on the Descent page, top right as well). Your 160/2000 is good for the ILS. If you want to be fully configured and stablized at the marker, then be at 160/2000 at least 3 miles from the marker by making a Along-track waypoint and putting the restriction there. :( You should be able to keep VNAV ingaged all the way to glide slope capture. Remember to reset MCP altitude to 2000 and push VNAV and it should continue the descent if VNAV was disengaged. You must be right on speed in this simulation for VNAV to engage at or below 10000 feet, use speed brake, thats what its for.c) First understand that VNAV Path is slaved to the Path. It is the pilots responsibility to control the speed. The FMC will Add Thrust if a headwind last longer than expected to stay on the path or it will dive to stay on the path if the headwind component is less than predicted. You may have to apply speed brakes if it dives to control the airspeed. The TGT SPD is used for planning purposes only. The FMC will only apply thrust if the speed gets too slow. To meet STAR airspeed restrictions, you may need to use the speed brake to make large airspeed reductions. This is normal.Also, there are three engine idle speeds, ground minimum, flight minimum, and approach idle. They are automaticlly controlled by the EEC's. Approach idle will have the highest N1, N2 idle RPM. These idle speeds will be affected by flaps, altitude and anti-ice usage. So yes, a higher idle can be expected in flight.Floyd

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Many thanks Floyd, very clear!!!For Lenny: yes, simetimes I can see the 'overspeed disconnect' message in FMC DES page. What does it mean?Andrea

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http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchQUESTION: What is the difference between a VNAV PATH DEScent and VNAV SPEED DEScent?ANSWER: In a PATH DESCent the aircraft will maintain the PATH without concern for the speed, it is the pilot's job to control his speed during the DEScent. For the SPD DEScent, the aircraft will maintain (i.e. PITCH) the target SPEED selected on the DESCent page without regards to the PATH. The pilot can use the speedbrakes or throttle to try to maintain the path if desired. Also, in a SPEED DESCent the aircraft will honor all waypoint restrictions by temporary level off until it passes the waypoint's original point on the path and resume DEScent.QUESTION: What happens in a DEScent if the aircraft overspeeds?ANSWER: The aircraft will be able to stay in VNAV until 1 knot prior to the barber poll, at which time the AFDS reverts to LVL CH. Below the airport restriction altitude (240/10000) it will disconect at 15 knots above the VNAV target speed. You MUST manage your speed with spoilers or go active SPD DEScent. The aircraft will honor speed retrictions IF it's possible to meet the restrictions, VNAV can only handle a certain *angle* before it will disconnect, below 10000 I think it's 6 degrees so plan your restrictions within the proper criteria...[h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/betaimg.jpg

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