Two quick questions about two flights
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Was on a L-1011 Tristar coming back from Italy inbound to Gatwick some years ago on final approach about 15 minutes out from landing. The engines went from normal tone to silence the aircraft dropped this went on a few times, with one of the cabin crew looking alarmed and with some of the pax calling out. This was followed by a heavy landing.
Was on a L-1011 Tristar coming back from Italy inbound to Gatwick some years ago on final approach about 15 minutes out from landing. The engines went from normal tone to silence the aircraft dropped this went on a few times, with one of the cabin crew looking alarmed and with some of the pax calling out. This was followed by a heavy landing.
The term flight idle, and its cousin ground idle, are a bit of a misnomer because (particularly on big fan engines) a fair amount of thrust is still being produced at those settings (ask any widebody tug driver about pushbacks!).
But it's not enough thrust to maintain level flight - the only way you're going to go with flight idle selected is down, which happily is what you want to do as you approach your destination.
In fact the Holy Grail nowadays, for environmental reasons, is to complete a Continuous Descent Approach (CDA) using flight idle all the way from ToD to the threshold. Needless to say, that involves both careful planning and, crucially, the active cooperation of ATC, but it's certainly doable.
In the bad old pre-CDA days, descent and approach would typically include descent segments at flight idle interrupted by periods of level flight (for which the engines would have to spool up again). That's what your pilot would have been doing.
Here's a good intro to CDAs from Eurocontrol: A guide to implementing Continuous Descent
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The two things you experienced (engines at flight idle and the heavy landing) aren't necessarily linked.
The term flight idle, and its cousin ground idle, are a bit of a misnomer because (particularly on big fan engines) a fair amount of thrust is still being produced at those settings (ask any widebody tug driver about pushbacks!).
But it's not enough thrust to maintain level flight - the only way you're going to go with flight idle selected is down, which happily is what you want to do as you approach your destination.
In fact the Holy Grail nowadays, for environmental reasons, is to complete a Continuous Descent Approach (CDA) using flight idle all the way from ToD to the threshold. Needless to say, that involves both careful planning and, crucially, the active cooperation of ATC, but it's certainly doable.
In the bad old pre-CDA days, descent and approach would typically include descent segments at flight idle interrupted by periods of level flight (for which the engines would have to spool up again). That's what your pilot would have been doing.
Here's a good intro to CDAs from Eurocontrol: A guide to implementing Continuous Descent
The term flight idle, and its cousin ground idle, are a bit of a misnomer because (particularly on big fan engines) a fair amount of thrust is still being produced at those settings (ask any widebody tug driver about pushbacks!).
But it's not enough thrust to maintain level flight - the only way you're going to go with flight idle selected is down, which happily is what you want to do as you approach your destination.
In fact the Holy Grail nowadays, for environmental reasons, is to complete a Continuous Descent Approach (CDA) using flight idle all the way from ToD to the threshold. Needless to say, that involves both careful planning and, crucially, the active cooperation of ATC, but it's certainly doable.
In the bad old pre-CDA days, descent and approach would typically include descent segments at flight idle interrupted by periods of level flight (for which the engines would have to spool up again). That's what your pilot would have been doing.
Here's a good intro to CDAs from Eurocontrol: A guide to implementing Continuous Descent
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Aircraft Energy States and Delayed Descent
1) Flying LAX to DFW on Monday, about 45 minutes from landing the aircraft suddenly slowed by about 20 knots. I thought we were actually starting an early descent, but checked the flight map on the IFE and saw we had slowed but not descending. About a minute or two later we sped up again. What might be the reason for this - sequencing?
Sometimes, ATC restrictions mean that the crew cannot get a clearance to descend at the optimum point. The aircraft is then above the profile and has more energy than would ideally be required.
The crew could just use speed brakes when they get the descent clearance, but this isn't particularly smooth or fuel efficient. So what the crew could do is reduce the aircraft's airspeed - thereby reducing the kinetic energy of the aircraft. They would then accelerate once the descent was initiated.
So the most likely reason for the behaviour was that the crew could not get a descent clearance from ATC - rather than reducing thrust and going down, they reduced thrust and slowed down!
We must be conscious that FlightAware and FlightRadar24 are both amateur products, done as well as they can, which use crowd-sourced data lifted from aircraft transmissions, plus an amount of interpretation. They do not have the accuracy of the professional systems. Five minutes looking at the track of aircraft on final approach to a runway, some aligned, others plotted coming in several miles offset, will tell you that.
The Tristar, designed in the late 1960s, had FOR IT'S TIME a surprisingly sophisticated, only partially computerised, Flight Management System, where you could put in a waypoint and an arrival time and it would fly the most efficient speed profile, to the second ! Literally. As the crew got various descent clearances it would be working all this out. Nothing unusual in 2018 but for a design from nearly 50 years ago, it was pretty nifty.
Some of the designers had come from Lockheed military projects, as Lockheed had not done a commercial airliner for a decade, but other team members were ex-Hawker Siddeley from Hatfield, where Trident development was running down and they had more good ideas than job opportunities. These personnel were part of the "brain drain" from Britain to the USA which politicians spoke about at the time - but whose stop-start procurement approach never ensured any career opportunities for them.
Was on a L-1011 Tristar coming back from Italy inbound to Gatwick some years ago on final approach about 15 minutes out from landing. The engines went from normal tone to silence
Some of the designers had come from Lockheed military projects, as Lockheed had not done a commercial airliner for a decade, but other team members were ex-Hawker Siddeley from Hatfield, where Trident development was running down and they had more good ideas than job opportunities. These personnel were part of the "brain drain" from Britain to the USA which politicians spoke about at the time - but whose stop-start procurement approach never ensured any career opportunities for them.
