Flying faster because of decreasing winds

[SR71]

Which surely amounts to about the same thing (protecting the IAS), just by different routes?

The OP wanted to fly the Airbus paradigm in his Boeing.

The Boeing proponents said, "Why?"

The Airbus proponent(s) said "Because its better. You protect IAS by flying a mini GS. You don't have de-stabilising thrust inputs late in approach."

(Not that I fly the Airbus, but are Airbus pilots and their machine so cool as to not bother to add thrust even if they did fly through a shear?)

The Boeing proponents said "We protect IAS by protecting IAS. Whats the big deal?" (Not many of us still here can say it hasn't worked for us...even BOAC, and by anecdotal accounts, he has been around a while.)

And then everybody got confused...

As for removing the mental maths, thats mental.

[Chris Scott]

Excellent one, Mark1234! All correct.

Quote from galaxy flyer:
I don't know if we invented "managed IAS", but the USAF uses something like this on its heavy transports. Originally, it was computed by the flight engineer, using approach TAS adjusted with current tower winds to calculate a "reference GS", the pilots then added enough knots to fly the plane at a groundspeed that was equal to the "reference GS". Later, it was automated thru the FMSs which did the calculated and displayed the "reference GS" and produced an aural warning, if the actual GS was less than reference GS.
It came out of windshear accidents and the ability of INS systems to show real time ground speeds. I thought it was useful for aircraft which have high momentums and low excess power-the C-5, for example. That said, we still had prohibitions about operations in windshear and TRW conditions.
[Unquote]

Thanks for answering my question (in post #5), and I think you have covered about two-thirds of the whole GS-mini subject in just two paragraphs. It confirms my contention that the technique predated the A320. As they say, there is nothing new under the sun.

What you describe, once it had been automated, sounds pretty close to Airbus's "managed" IAS.

You hit the nail on the head when you talk of aircraft that have little surplus power/thrust, like your C-5. Without comparing typical thrust-to-mass ratios on various aircraft, I guess heavy B707s are also underpowered, and presumably B-52s.

B707s were retrofitted with INS eventually, but I don't remember Boeing offering guidance of this kind, which would have been useful. The only "additive" we used to apply to the "bug" (VREF) was a mental one (no objection to that) based on the surface wind (half wind speed + gust, up to a maximum of 20kt). Can't comment on early 747s; but framer tells us that "Qantas boeing crew use RGS or reference ground speed. It basically provides them with a ground speed they don't go below. Works well."

It's only fair to admit that most twins, including BOAC's and SR71's B737, have the luxury of a good thrust-to-mass ratio in the all-engine case. Maybe that is why they can stick to the old version of energy management on the approach: simply chasing an IAS that is based only on VREF, plus an increment for the wind on the surface – which wind may be zero.

[Chris Scott]

Like autoflight, I am increasingly dismayed at the difficulty that so many otherwise intellectually-bright forumites appear to be having to grasp what is essentially a simple concept: the importance of protecting the all-important IAS by not allowing the GS to fall too low when a negative windshear is known to be ahead.

The fascinating – but essentially esoteric – discussions about the precise definitions of inertia, momentum, and kinetic energy are unnecessary in this context, although they might well be worthy of a separate thread. On this one, they amount to little more than fog-inducing semantics. I'm wondering if, in one or two cases, they are inspired by an element of perversity of the "not invented here" variety.

The sceptics constantly emphasise the importance of IAS, and seem to recognise that it can suddenly fall dangerously, due to a loss of headwind; as described by VinRouge (post #27). Their mantra is roughly this: IAS is the only thing that matters; so we must concentrate on it exclusively, and ignore the GS. Wizofoz (post #35) seems to be implying that we, on the other hand, are advocating that GS is more important than IAS.

This is a perverse misrepresentation of my previous posts, which clearly state that the target IAS is always the higher of: the conventional approach IAS (on the one hand); and the IAS which delivers the calculated minimum GS (on the other). So we are always at an equal or greater IAS than he is.

To save readers looking back 3 days, let me remind you that in my first post (#5), I wrote: "...lift requires IAS."
I then invited sceptics to look at IAS from a fresh perspective –
"IAS = GS plus headwind-component (sea-level/ISA). Shortage of (GS) can only be corrected by applying extra thrust; for a period of time. On a bad day at the office, that time may not be available."

Two days ago, in post #16 –
"You imply that we are ignoring the all-importance of IAS. On the contrary: IAS is precisely what we are trying to conserve."
and –
"The GS-mini concept protects IAS by constantly offering the pilot an IAS target (managed speed) which results from:
the higher of VAPP and the IAS required to achieve the minimum GS."


Quote from SR71,
I've touched down in a light 737 at a GS of <90kts on a day when it was gusting 65kts. I didn't even think about GS. The only thing I seek to preserve on finals is IAS. If I fly through a shear, I need to regain IAS surely, not GS?
What am I missing?
[Unquote]

Does he want an honest answer? Seriously, though, the secret is to anticipate the shear, if you can predict it is going to happen. [If you cannot, that's another topic.] We are not discussing the situation where the wind is strong and gusty all the way down to and including the threshold; it is the sudden predicted suspension of a headwind that concerns us.

SR71 will continue concentrating manfully to regain his target IAS, which he need not have lost hold of in the first place. While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

Mark1234 describes the advantage of (automated) GS-mini: as the headwind falls, taking the actual IAS with it, the target IAS normally falls by the same amount (but never below the threshold IAS). That is because the inertia of the aircraft protects its GS (unlike its airspeed). And remember, TAS = GS + HWC. The minimum GS is the threshold TAS minus the headwind component of the programmed surface wind. IAS and TAS are the same at sea-level/ISA, of course, but usually not elsewhere. The system corrects automatically for the conversion of target TAS to target IAS, which is one of the awkward things to do manually, and therefore invaluable.

[Wizofoz]

Chris, No, I think it's you that unintentionally misrepresented my position.

I've kept out of the minimum GS debate entirely. I understand the concept and have no doubt it works. I shall therefore, when on approach.....Follow my companies SOPs and do as I'm told!! If I'm ever put in a policy making position, I will revisit the whole matter and...Follow the manufacturers recommendations!!

All I have been doing is trying to do is point out several conceptual fallacies to which you seem to subscribe, encapsulated by one of your first statements:-

Inertia is a function of GS, not IAS.

Which was untrue at several levels, not least of which being you didn't know the difference between Inertia, Momentum and Kinetic energy, and that you constantly allude to an aircrafts ground speed somehow effecting it's aerodynamic performance.

The only relationship that effects the aircraft is between it and the air around it. Carrying extra airspeed to allow for changes in that relationship is valid. Basing the amount to carry on a fixed datum like the earths surface is also valid. Making pseudo-scientific statements about "Kinetic Energy" and how it should be based on the earths surface is not.

The fact that you still don't get it is shown by your mocking tone towards SR71 when you said-

SR71 will continue concentrating manfully to regain his target IAS, which he need not have lost hold of in the first place. While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

Dude, it's that unstable atmoshere we need to keep flowing over our wings, and it is are IAS that is a measure of that flow.The amount you need to change (or, in your method, the extra you need to hold in the first place) is equal to the amount the air is going to change it's velocity relative to your aircraft.

It was you who started (incorrectly) throwing scientific terms around, don't get snitty with someone for correcting you (BTW framer, thank you!).

I also note that you are a greater authority than Boeing on how to fly Boeings, and anyone who doesn't fly as you recommend is open to mockery and criticism

[Meikleour]

Chris,
I admire your perseverance in trying to open the minds of the `determindly closed`! Some people will just never get it. It`s a bit like the advocates of wing warping saying that ailerons `will never catch on`

Bon chance mate.

[Wizofoz]

Meik,

I'd be interested to know who you think is showing a closed mind here and how. I for one have stated that I understand the concept of GSmin, and agree it would work. I just don't go around ignoring my Boeing approved and company mandated procedures because someone on PPRUNE made a persuasive argument.

I'll happily fly a min GS approach- The day it appears in my ops manual!!

[Chris Scott]

Thanks, Miekleour.

Quote from Wizofoz:
I've kept out of the minimum GS debate entirely. I understand the concept and have no doubt it works.
[Unquote]
Why? It was central to the topic. It was the main element of Olendirk's original post, which was a thoughtful request for an explanation of how the technique works. His question was effectively ruled out as heresy by BOAC (post #3).
Referring to anyone who advocated the technique, he wrote:
"ignore them - they are mad."
Just to ram the point home, he wrote:
"IF you choose to do it, the info is on your EFIS, but I suspect any Captain with half a brain would then take control and have you sectioned - I would."

This paternalist scolding seemed to me to be less than helpful. The concept needed to be explained, which I attempted to do in common cockpit parlance. In Physics terminology, of course, my use of the word "inertia" was wrong – as Wizofoz (and others) pointed out, and I quickly accepted. Since then, the "debate", as he calls it, has consisted mainly of nit-picking.

As Wizofoz understands the concept – and can presumably explain it better than my feeble efforts, would it not be more helpful to do so? There's still time...

Quote from Wizofoz:
...you constantly allude to an aircrafts ground speed somehow effecting it's aerodynamic performance.
[Unquote]
Rubbish. Any quote?

Quote from Wizofoz:
...don't get snitty with someone for correcting you
[Unquote]
Examples?

Quote from Wizofoz:
I also note that you are a greater authority than Boeing on how to fly Boeings, and anyone who doesn't fly as you recommend is open to mockery and criticism
[Unquote]
No. I recommend that pilots remain within the limits of their companies' SOPs. galaxy flyer and framer have provided evidence that manual versions of the concept have been in use elsewhere, since the introduction of INS. Although I attempted to explain a possible procedure to Olendirk ("D.I.Y. GS-mini?", post #17), I included several caveats, and ended it with a strongly-worded warning not to deviate from SOPs. Since then, I have added:
"It's only fair to admit that most twins, including BOAC's and SR71's B737, have the luxury of a good thrust-to-mass ratio in the all-engine case. Maybe that is why they can stick to the old version of energy management on the approach..."

The difference between me and many of the pilots on PPRuNe is that I spent 17 years flying approaches on a variety of jet transports, including the underpowered B707, using IAS with SOP-increments, and ignoring any GS read-out. I later spent 14 years flying GS-mini-equipped twins.

The B707-320, with a MLW of 112T and only about 30T (spare us a lecture about Newtons, etc.) of rated thrust, could have benefited from the technique more than most. There is no doubt that automated GS-mini, used iaw SOPs, is a useful and protective system. It is particularly advantageous in the engine-out case.

But both pilots and the A/Thr need to avoid the mistake of using the "managed" IAS as a minimum speed, rather than a target.

[BarbiesBoyfriend]

I'd say thinking about your GS while on approach is a bit silly.

All that matters is your IAS and the wind.

On a windy day, if I ve got 40kt on the nose and the surface wind has been passed as 10kt, I know 30kt of HWC is going to disappear at some point. Therefore I fly a bit faster!

Got 10,000 hours now and never had a negative windshear- so it works!

[Wizofoz]

Rubbish. Any quote?

HERE:-

Inertia is a function of GS, not IAS

HERE:-

Shortage of inertia (GS) can only be corrected by applying extra thrust

and HERE:-

As you say, no velocity is absolute; it has to be relative to something. However, astronauts excepted, pilots and humans usually measure it in relation to the local surface of mother earth.

You meant momentum, but were still wrong.

Examples?

Here:-

If it's "Horlicks" to state that, for a given mass, inertia (kinetic energy) is a function of GS, perhaps you can tell us what else? IAS?

(Actually, that belongs in both columns)

And most notabley Here:-

While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

If you had simply given an explination of Gs Mini- A way of allowing for windshear by carrying sufficient IAS to allow for it, referenced to a ground speed, all would have been fine. Your delving into iffy physics was always going to be challenged- it is Tech Log after all.

BTW, what happens to an aircraft flying with a large headwind if it quickly turns 180Deg??

[Port Strobe]

So in summary Chris you've been right all along. You agree that we're all agreed we understand how GS mini works, some of us have learned a little about inertia, momentum, kinetic energy of the translational variety and their lack of interchangability, and in the future we'll all fly approaches based on a minimum reference grounspeed to save us from adding thrust to maintain the IAS as this is safer than having an increasing groundspeed throughout the approach. However the practical ramifications of this discussion are we'll still go to work and do as we're told by the manufactuer and any deviations from this approved by our respective employers which are authorised by their NAA all underpinned by airmanship questioning whether or not it is sensible to do so in the present and expected conditions, be they meteorological, proximate traffic its sequence or whatever. Which is a long way of saying what I said on the first page in response to the initial question, when it's managed speed faffing with the command speed then let it do so until you're content however until that day arrives then do as instructed. Which you said you're also in agreement with. Agreed we're all agreed?

[Meikleour]

Wizofoz,
What makes you think I was referring to you?!

If your main arguement is `comply with one`s own company SOP`s` then we are in complete agreement! HOWEVER that was not the reason for the original thread. On the three Boeing types I have flown (B707, B737, B747) the maximum Vref increment was +20kts. I also flew with one operator who used the minimum reference ground speed concept on these types. The problem arises when the expected change in headwind component decreases by more than that amount. To berate Chris about his use of scientific terms and to quibble about frames of reference misses to whole point of the arguement! An Airbus, using mini-GS arrives over the threshhold at a SUITABLE GROUND SPEED and a SAFE IAS!

QED

[SR71]

Chris,

I'm bowing out at this point...

Like the Wizard, I understand what the concept you allude to is seeking to guard against but I (also) objected to your use of terminology and the constant reference to GS.

To have a sensible discussion, one has to use the right terminology. I'm sure you agree.

I let you know early on I was a pedant.

[john_tullamarine]

might be a suitable time for some of the folks to have ten deep breaths .. the forum isn't about sheep stations .. only looking for reasonable and rational discussion on the topic. If this one or that has a different view, that's fine .. as always, the aim is to play the ball, not the player.

[krujje]

as always, the aim is to play the ball, not the player

but are we measuring the velocity of the ball relative to the players, the court, the air, the earth, or the sun...?
ah! forget it...

[autoflight]

I flew military & airline for 38 years and only recognised a microburst one time. It seemed that the initial outward wind was about 80 knots. If that was on your final approach and you ignored all the evidence, expect a near instantaneous loss of 160 knots of IAS. Unrelated to the loss of speed would be an increase ROD due to the rapidly decending air. Please nobody tell me this is a survivable event! Avoidance is the only reasonable course.
I am also concerned that a few jet pilots out there still don't understand that an indication of impending loss of IAS is when G/S on final is lower than speed calculated using tower reported wind. A moderate shear will show as a G/S perhaps 10 - 15 knots less than the calculated touchdown G/S. This might not be an indication of a microburst. If you expected a G/S of 120 knots and at 500 ft, with a stabilised approach, it is 70 knots, I would call that very significant windshear, probably with worse to come. This could be a MB. All your worries about how your kids will turn out, will your marriage last, will you have a successful retirement, will probably disappear with you, your crew and pax in a smoking hole in the ground short of the runway.
You don't have to actually fly G/S. Just make sure you don't go much below it. If you're not able to force yourself to do this because you were trained to fly IAS, at least keep an eye on it to assist in identification of perilous conditions.

[BOAC]

Well, I 've been doing JT's 'deep breathing' for a couple of days and returning now to read the thread I have to say that in my opinion 'Port Strobe' has said it all. As I said to Olendirk on Post #3,

Originally Posted by PS

However the practical ramifications of this discussion are we'll still go to work and do as we're told by the manufactuer and any deviations from this approved by our respective employers which are authorised by their NAA all underpinned by airmanship questioning whether or not it is sensible to do so in the present and expected conditions, be they meteorological, proximate traffic its sequence or whatever.

- i.e. when your 737 operating company TRAINS you to fly g/s on finals, learn how to do it and do it well. Until then, fly your company procedures - and conform to ATC speed request, of course, as always.

[autoflight]

It is quite rare for me to specifically identify those with a contrary view, but in the interest of flight safety I ask that less credibility be given to the entrenched opinion of those absolutely opposed to G/S considerations.

[Capt Pit Bull]

Looks like I'm a bit of a 'johny come lately' and missed most of the good bits!

One problem here is that its very common for people to build their understanding of principles of flight on a foundation of dodgy Physics. Most of the issues have been thrashed out above. I know it might sound pedantic, but things like mass, inertia, momentum and kinetic energy are often not just slightly different but are truly radically different quantities.

I think momentum and kinetic energy have been well dealt with above. A brief summary:

Momentum. mv. A vector quantity. Conservative (in a given system, total momentum is always conservative, this is intimately connected to Newton 2 and 3). Pitbull top tip: Use changes of momentum to figure out how long a TIME it takes for a force to cause a change.

Kinetic Energy. 1/2mv^2. A scalar quantity. NOT conservative (total energy is conservative, any given form isn't). Pitbull top tip: Use changes in Kinetic Energy to figure out how long a DISTANCE it takes for a force to cause a change.

So we can see, they are different in pretty much every way. Don't let the fact they both have an M and a V in them fool you into assuming they are very similar - they aren't!

What about Inertia and Mass then? Not sure this has been properly dealt with. There are two aspects to mechanics, translational and rotational. Everything above (I think) was about translation, i.e. an object moving around in its frame of reference. However, there are almost identical concepts relating to the rotation of objects.

e.g. We know (Newton 1) an object will maintain a given velocity unless acted upon by an unbalanced force. The rotational equivalent is that an object will maintain a given rotational speed and orientation in space unless acted upon by an unbalanced Torque. There are equivalent concepts for momentum and angular momentum, kinetic energy and rotational energy and so on.

Inertiais a term that applies to both parts of mechanics. It is, in general, the reluctance of a body to change what its doing. The reluctance of a body to be moved is its mass. However an objects mass does not tell us much about the reluctance of a body to change its rotation. For this we need a quantity that describes not just the mass but also the distribution of the mass (remember your basic gyro theory?). This is the moment of inertia.

So, Inertia is a general term that encompasses both mass and moment of inertia.

As such, mass and inertia are not strictly identical to one another, but rather mass is a subset of inertia.

However, if you are only talking about translational mechanics then you can petty much get away with using the terms interchangeably.

Clear as mud?

pb

[BOAC]

Originally Posted by a/f

I ask that less credibility be given to the entrenched opinion of those absolutely opposed to G/S considerations.

- if that salvo was fired at me, you should aim more carefully. Please note I have never said I am 'opposed to G/S considerations', merely that I would be tempted to have an F/O placed under restraint in a 737, or use the Rainboe rolled-up newspaper technique if he/she flew that way in contradiction to company procedures, and I would personally deliver him/her to SATCO for a whipping if he/she neglected to fly ATC requested speeds.

I happen to think it is an extremely valid way to approach approaching and a spiffing idea, OK? Jolly good wheeze for an Airbus, Ginger.

[autoflight]

ATC requested speeds are nothing to do with avoiding dangerous windshear. Avoiding windshear difficulties is not type or company specific airmanship. Narrow minded and outdated company policies are items requiring official adjustment rather than blind obedience. Anyone who has made thousands of Prunne posts can surely put an approach speed proposal to his company rather than threatening F/O. Is this sufficiently directed?
Great post Olendirk. This subject obviously needs to be out there, but this is my last word.