Basic Aeronautical Knowledge questions

[43Inches]

Originally Posted by swh

Does not matter what you think the errors are, ATC can see what is selected on the glareshield via ADS. If you have selected 185 and you were instructed to maintain 180, they can see that. Just like they can see if you were instructed to climb to FL170 and put in FL190 on the glareshied they can see that.

Airliners transmit the data, it’s up to individual states if their ATC units use it.

NATS for example publishes speed compliance reports to operators for LHR and DXB, they know what pilots have selected.

A few scenarios where the set/bugged number is not accurate, 1 in Australia ATS can't see the set IAS, 2, I could descend in VS and disable IAS control, meaning whats in the window/bugged don't matter or 3, totally ignore the automatics and hand fly meaning all settings in the windows are just alerters and reference for the pilot. Lastly I could be flying something old that does not have IAS or Altitude settings transmitted via SSR at all, I know of a few types, esp turboprops still floating around that don't connect to said system. Also add that in some autopilot set ups I can select which input side the IAS comes from, so if the FOs side is under-reading I could select that side and get a higher speed than selecting the CPTs side.

[Clinton McKenzie]

But you can’t hide your groundspeed, at least while in radar/SSR/ADS datalink range…

[swh]

speed,

Originally Posted by 43Inches

A few scenarios where the set/bugged number is not accurate, 1 in Australia ATS can't see the set IAS, 2, I could descend in VS and disable IAS control, meaning whats in the window/bugged don't matter or 3, totally ignore the automatics and hand fly meaning all settings in the windows are just alerters and reference for the pilot. Lastly I could be flying something old that does not have IAS or Altitude settings transmitted via SSR at all, I know of a few types, esp turboprops still floating around that don't connect to said system. Also add that in some autopilot set ups I can select which input side the IAS comes from, so if the FOs side is under-reading I could select that side and get a higher speed than selecting the CPTs side.

ADS-B does not transmit IAS unless the GNSS data is unavailable, GNSS easting speed, GNSS northing speed is the priority, from that the ground speed and true track is resolved using trigonometry. As a backup the aircraft will transmit IAS and heading if that data is made available to the transponder.

The data packet will also transmit a number of other parameters from the glare shied and FMC, ATC may choose to use this data, it may choose not to. The aircraft sends all the data it can, and the ATC system decodes what it wants from the raw data packet.

The raw data packet is still in the system, ATC can post process the data packets to see how the aircraft is being operated (this is what NATS to do arrival speed compliance). If you choose to turn everything off that’s fine, that can also be seen.

I would be very surprised if ASA does not look at that raw data as well as the noise measurements for arrival and departure tracks to understand how aircraft are being operated in response to noise complaints and amend procedures accordingly.

[swh]

Originally Posted by le Pingouin

TAAATS alerts when there's a mismatch between the cleared level in the label and what the pilot has dialled in as the assigned level, it just doesn't show what the pilot has dialled in.

Dont understand that sentence.

[le Pingouin]

If we have say F150 set as the cleared level in TAAATS and you set anything different we get an alert. We don't see what you have set, just that they aren't the same.

[swh]

Originally Posted by le Pingouin

If we have say F150 set as the cleared level in TAAATS and you set anything different we get an alert. We don't see what you have set, just that they aren't the same.

Ok understand now, that is just what the grown ups have decided you need to see, the system is actually more capable than that. Other countries using topsky displays different data.

[Clinton McKenzie]

Originally Posted by le Pingouin

To add the display functionality to TAAATS would likely cost a mozza and would be rather hard to justify given a new system isn't too far away - they're nice to haves rather than must haves.

What “new system” would that be and about how “far away” is not “too far away”?

[43Inches]

I was not talking about displayed actual IAS, I was talking about the controller knowing what is in the glareshield window, whether that is Altitude or set IAS. There are still many RPT aircraft that don't have autopilot settings linked to the ADSB signal, or lack a settable IAS window all together. So even if Airservices activated this it would not display as the aircraft is not sending the information. Most of the older turboprops would fit into this group, that is the majority of RPT turboprops in Australia (pre -400 Dash, SAAB and Metro, F50), the jet fleet is more modern so not many would be old enough to not have the link.

[le Pingouin]

OneSKY is the new system - CMATS is the control system component and is a combined civil and military system. The glossy brochure says the rollout to military units starts this year and to civil units starts next year.

[Clinton McKenzie]

A ‘partnership’ between Air Services and Defence with Thales on the other side. What could possibly go wrong?

The not-so-glossy Auditor-General’s report on its assessment of whether the contract for the acquisition of the system represents value for money concluded:

10. Important changes were made, after the successful tenderer was selected, to the timeframe for delivery, scope of work, type of contract and price. An appropriate governance framework was established to evaluate whether negotiations had resulted in contract terms that represent value for money. Shortcomings in the application of that framework mean that value for money has not been adequately demonstrated.11. If the current contracted timeframes are achieved, there will be a more than ten year delay (from 2015 to 20265) in the replacement of the existing separate civil and military systems compared with the timeframe envisaged at the start of the procurement process. The capability baseline for the new combined system was established in advance of issuing the Request for Tender through appropriate engagement with industry. Delays with tender evaluation activities were exacerbated by even longer delays in the negotiation phase. Negotiations took so long that the offer submitted by the successful tenderer expired and the lives of the existing separate systems needed to be further extended. Negotiations also resulted in a late change in the contracting model from the one that had been presented to the market in June 2013.

12. There is inadequate assurance that the acquisition price is consistent with a value for money outcome:

• For the June 2016 offer, a comprehensive evaluation report was produced that included a clear conclusion that value for money had not been achieved. This was principally due to concerns about the $1.449 billion estimated acquisition cost.
• Through further negotiations, changes were made to delivery timeframes, the scope of work and the contract model, leading to a September 2017 final offer (with an estimated target price of $1.23 billion with the ceiling price to be 10 per cent higher) followed by further negotiation on scope, price and commercial terms. An evaluation report addressing each criterion, the expected total cost of ownership and whether the negotiated outcome represented value for money, was not prepared by the CMATS Review Board (CRB) and provided to the Airservices Board to inform the decision to sign the acquisition contract. Rather, the Board was provided with a report prepared by the Lead Negotiator6, who was not authorised to and did not undertake a full evaluation of the offer.7 The records of the relevant Board meeting do not identify or discuss the provision of the February 2018 Lead Negotiator’s Report8, and do not outline the value for money considerations of the Board.

13. Price risk is dealt with in the terms of the acquisition contract.

[Footnotes omitted.].

But I’ve strayed way too far from the subject of this thread. I anticipate that OneSky will become the subject of its own thread, sooner or later.

[Clinton McKenzie]

Interestingly, the only speeds I heard mentioned by Centre today were "TAS" (asked a pilot the current TAS of his aircraft - a PC12 I think), "normal speed" (resume normal speed) and "minimum speed" (reduce to minimum speed).

[le Pingouin]

We ask for "TAS" as that's what TAAATS uses in the flight plan to calculate estimates. If there's a significant difference between what's stored and what the aircraft is flying (e.g. when flying at a significantly different level, after airwork or just because you're not flying what you planned) then we'll get an alert due to the surveillance derived estimate and calculated estimate being too different.

[Uplinker]

Originally Posted by Clinton McKenzie

If 43 was told s/he's closing at 10 to 20 knots, despite having an IAS that's supposedly 10 knots less than the 'lead' aircraft, how could that have been determined other than by ground speed data from the aircraft? Is it just calculated from the position of and changes to their radar returns?

I'm trying to get my head around why the IAS method of separation is used when ground speed data is available to both the controller and the pilots. If the 'lead' aircraft has a groundspeed that's e.g. 5 kts slower than the 'trail' aircraft on the same track, why does ATC 'care' what their respective IAS indications happen to be if ATC knows their respective positions and groundspeeds?

(And thanks for you answers, le P. I'm learning stuff.)

I am not a controller, but if an aircraft has been assigned a Mach/IAS and they are catching up the one in front - as noted on your radar display - then assign the trailing aircraft a slower Mach/IAS. You don't need to know their groundspeeds. (Sometimes pilots don't set the requested IAS/Mach - sometimes ATC can see what speed they have actually set !!)

Re your second point; Aircraft are not designed to fly by selected groundspeed. There is no selection window or data box in the FMGS to select a groundspeed, and there are no groundspeeds dictated on SID and STAR plates. There is nowhere to set a groundspeed bug. If you think about it, it could be incredibly dangerous to do so - it could cause an aircraft to stall or overspeed if the winds were particularly strong tail winds or head winds.

We can select or program a Mach number or an IAS, because that is what the lifting and control surfaces 'feel'and react to. We are not cars on a road; we need to move through the air molecules at precisely known speeds to provide the lifting performance we need to stay aloft. (And, no, we are not going to get out our CRP-5's to work out what IAS we need to fly a groundspeed, then work it all out again when we change our heading !)

To know your TAS or groundspeed, you need accurate OAT probes and air data computers and some form of very accurate inertial or GNSS position determining computer. Not all aircraft will have this - certainly not all of the same accuracy. But all aircraft - even a basic Cessna 152 - have an IAS readout.
.

[Clinton McKenzie]

I am not a controller, but if an aircraft has been assigned a Mach/IAS and they are catching up the one in front - as noted on your radar display - then assign the trailing aircraft another 10kts IAS slower. You don't need to know their groundspeed. (Sometimes pilots don't set the requested IAS/Mach - sometimes ATC can see what speed they have actually set !!)

But the originally ‘assigned IAS’ should have been enough to resolve the potential conflict. Why wasn’t it? (The answer has a ‘G’ and an ‘S’ in it.) And what does the controller do if ‘assigning’ the trailing aircraft another ‘10kts IAS slower’ doesn’t solve the problem? If pilots don't set the requested IAS/Mach, the pilots are 'naughty'. But it's ultimately the ground speed and track that are gonna cause collisions that will kill people.

Re your second point; Aircraft are not designed to fly by selected groundspeed.

Of course not. But it’s a parameter that’s right there on those GPS and radar screens. Plus track.

There is no selection window or data box in the FMGS to select a groundspeed, and there are no groundspeeds dictated on SID and STAR plates. There is nowhere to set a groundspeed bug. If you think about it, it could be incredibly dangerous to do so - it could cause an aircraft to stall or overspeed if the winds were particularly strong tail winds or head winds.

I have thought about it. I understand that GS does not equal IAS, and I understand it’s air speed that keeps an aircraft in the air. But that’s precisely why an aircraft can have e.g. have a groundspeed twice its stall speed, yet still stall and, conversely, a groundspeed half its stall speed, yet still not stall and continue flying to eventually collide with another aircraft.

The ultimate point of this thread is that prosecuting a pilot for flying an aircraft so as to exceed VNE (an airspeed) on the basis of the aircraft’s recorded groundspeed is … what is the appropriate adjective: nonsensical? incompetent? malicious? Choose your own.

We can select or program a Mach number or an IAS. (And, no, we are not going to get out our CRP-5's to work out what IAS we need to fly a groundspeed, then work it all out again when we change our heading !)

I’ve obviously confused some people by not making clear that the point of this thread was not to suggest that pilots should ‘program’ or otherwise try to manage an aircraft’s ‘safe passage through the air’ by managing groundspeed. My apologies for the confusion. Managing groundspeed is about knowing and managing ETA and collision risk.

To know your TAS or groundspeed, you need accurate OAT probes and air data computers and some form of very accurate inertial or GNSS position determining computer. Not all aircraft will have this - certainly not all of the same accuracy. But all aircraft - even a basic Cessna 152 - have an IAS readout.

No Cessna 152 has ever been the subject of air traffic control instructions as to the IAS to be flown. At least not on the planet on which I live.

But every Cessna 152 pilot – or at least those who progress to cross-country navigation - should be able to work out TAS from IAS and temperature and pressure altitude. ‘Accurate’ instruments, including OAT measurements on Cessnas, have fat margins of error that don’t result in too many people going too fast or too slow, or getting lost, that often.

And very accurate GNSS position determining computers? I think there have been hundreds of thousands of aircraft flying around with them, for quite some time.

[Clinton McKenzie]

Originally Posted by le Pingouin

We ask for "TAS" as that's what TAAATS uses in the flight plan to calculate estimates. If there's a significant difference between what's stored and what the aircraft is flying (e.g. when flying at a significantly different level, after airwork or just because you're not flying what you planned) then we'll get an alert due to the surveillance derived estimate and calculated estimate being too different.

The "surveillance derived estimate".

Would that "estimate" be "derived" from location, groundspeed and track by any chance?

[le Pingouin]

I should have said a manually entered estimate rather than surveillance derived estimate because it could be calculated by the controller using a combination of ground speed and observed behaviour of previous traffic along the route (as in how aircraft speed changes over along the way), or it could have been provided by the pilot.

Ground speed has it's use but so do IAS and TAS.

[Uplinker]

Well, I have already suggested that without any record or tell-tale of IAS, (or the actual OAT or air density or wind speed around the aircraft) at the time, there is no case to answer - unless a wing or a flap fell off or something? Why not simply show your accuser the derivation of IAS, CAS, EAS, TAS, etc. and ground speed in a text book?

It is not impossible, but unlikely that two aircraft 5 or 10nm apart at the same level would experience markedly different wind vectors, (unless they were crossing a jet stream). You can get different winds at different levels of course, so at the same IAS an aircraft on approach could catch-up with a preceding aircraft on the glide-slope for example.

You would have to check with ATC but they have a mental picture of the winds on their traffic screen, and their screen software can show a prediction of where the aircraft will be in the next 10s, or whatever. We pilots sometimes get asked for a spot wind so they can update their mental model - or we report any particularly strong winds to them.

Beyond that I don't really know what the OP is on about. You sound as if you already know the answer, in which case, why ask us and then shoot our explanations down?

FWIW I was sometimes asked my IAS by ATC when flying C152s, and I remember waiting at the holding point at Dublin, EIDW, in a commercial jet when a poor sod in a C172 who had got lost was guided in to land on the main runway ! He was very apologetic, and Dublin ATC were brilliant - really understanding and helpful.
.

[le Pingouin]

Quite possibly because they don't know what it would be

[MechEngr]

Is there a link to the rule that would require/allow prosecution of a pilot for exceeding Vne? Apparently in the US doing so will void the airworthiness certificate, but not sure why it would end up as a criminal matter.

Also True Air Speed calculation requires knowing the temp, the pressure, and the humidity and is of little use to anyone if they have a GPS unit as TAS would otherwise be added to wind vector to find the Ground Speed. That's not an easy calculation to do as the humidity information is hard to come by.

Indicated Air Speed is a way of expressing the dynamic pressure available as used in Bernoulli's equation and is what the Vne limit is based on.

There should be a significant margin between the IAS and Vne during operation as at Vne there is no longer protection against gusts; the further from Vne the more tolerance for gusts. In practical use, the maker may leave further margin such that the wings might be wrinkled but remain attached airspeed excursions over Vne, likewise margin for the other Vne limiting factor - flutter onset for flying or control surfaces.

[Clinton McKenzie]

In Australia, up until recently the regulation was reg 138 of the Civil Aviation Regulations 1988, which required the PIC to comply with, among other things, all limitations in an aircraft’s flight manual (if one was issued) or set out in equivalent documents and placards (if a flight manual wasn’t issued). In essence: Vne is clearly ‘spelt out’ in the limitations section of the AFM/POH for most ‘modern’ aircraft and on some placard for ‘older’ aircraft.

Here's what reg 138 said when it was in force:

138 Pilot to comply with requirements etc of aircraft’s flight manual etc

(1) If a flight manual has been issued for an Australian aircraft, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out in the manual.

Penalty: 50 penalty units.

(2) If a flight manual has not been issued for an Australian aircraft and, under the relevant airworthiness standards for the aircraft, the information and instructions that would otherwise be contained in an aircraft’s flight manual are to be displayed either wholly on a placard, or partly on a placard and partly in another document, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out:

(a) on the placard; or

(b) on the placard or in the other document.

Penalty: 50 penalty units.

(3) An offence against subregulation (1) or (2) is an offence of strict liability.

Note: For strict liability, see section 6.1 of the Criminal Code.

That’s been replaced by Civil Aviation Safety Regulations 1998 reg 91.095:

91.095 Compliance with flight manual etc.

(1) This regulation applies in relation to the operation of an aircraft during the following period:

(a) from the earlier of:

(i) the time the aircraft’s doors are closed before take‑off; and

(ii) the time the flight begins;

(b) to the later of:

(i) the time the aircraft’s doors are opened after landing; and

(ii) the time the flight ends.

(2) The pilot in command of the aircraft contravenes this subregulation if the pilot in command does not comply with either or both of the following:

(a) the aircraft flight manual instructions for the aircraft;

(b) any conditions specified in the aircraft’s certificate of airworthiness or special flight permit.

(3) A person commits an offence of strict liability if the person contravenes subregulation (2).

Penalty: 50 penalty units.

Interesting point you make about the airworthiness certificate. One would have thought that exceeding Vne would at least entail a special inspection.

As to any difficulty of calculations of TAS, good luck doing any sensible flight planning on the basis of IAS! Every flight plan I’ve ever completed and filed – either on paper or electronically – has fields that include “TAS” and “WIND” from which a “HDG” and “GS” are calculated, so as to achieve the desired “TRK” and derive “ETI” and “EST” for each leg and waypoint. No “IAS” field to be found!

The inputs on the ‘wind’ side of a prayer wheel are TAS and WIND direction and speed.

The ‘steam driven’ ASI in the bugsmashers I fly have an adjustable scale to input pressure altitude and OAT so that the ASI pointer points to …. TAS. The Cessna 172 in which I did my ‘navs’ 30 plus years ago had an OAT gauge on the end of one of those ‘vent tubes’ at the top corners of the wind shield.

Of course the TAS for planning usually comes out of table in a POH and the winds are just a forecast and the graduations on the ASI adjustable scale are hundreds of feet and many degrees ‘fat’, but as I say: How else are you going to plan? And back when we had to report a revised estimate at a waypoint that was more than 2 minutes different from the one in the plan we’d filed, only GS and TRK mattered. For me, IAS has only ever been about not breaking the wings off, not stalling and not extending/retracting things at too high a speed. (I remember a couple of occasions when unexpectedly poor climb performance (IAS and VSI) was symptomatic of partially-retracted undercarriage – CB ‘popped’ – but very rare.)