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Selected Altitude input during SIDs

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Selected Altitude input during SIDs

Old 4th Mar 2007, 17:55
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Selected Altitude input during SIDs

Greetings,
I'd like to ask a technical question that arises as my Air Traffic Service Provider considers the concept of P-RNAV extended SIDs going to Flight Levels in the near future. I want to ensure that we understand what impact, if any, this may have on the downlinking of Selected Flight Level through Enhanced Mode S.
The question is this, what value is input into the Selected Altitude Window on the Mode Control Panel when departing on a SID that features a step climb? Is it (a) the altitude of the first step or (b) the final altitude / level associated with the SID?
For instance, if I have a SID that is published to finish at an altitude of 6,000ft, but that has step climbs at 3,000í and 4,000í due to interaction with other routes, do you put the 3,000ft or 6,000ft value into the Selected Altitude Window?
If possible, can you please include the type of aircraft that your response relates to, and if possible, the operating company as well as I suspect that procedures will vary from organisation to organisation.
Many thanks.
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Old 4th Mar 2007, 18:22
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BA - 737

Delete restrictions from the FMC and put the first alt constraint in the ALT window - Your example 3000'.
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Old 4th Mar 2007, 18:39
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Ditto but FMC restricted SID altitudes left in place until cleared above them.

I would be surprised if ANY company put the final cleared level in the window.
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Old 4th Mar 2007, 19:06
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Depends on specific airplane/equipment and airline SOP...

In the 744, for example, in VNAV mode the restrictions are programmed into the FMS automatically. If given a "Descend via STAR" or "Climb via SID" clearance to an altitude or flight level, the cleared altitude MAY be set in the MCP if the crew verifies all restrictions are in fact programmed and show in the CDU. As indicated by others above, many airline SOPs require that the intervening restrictions be set in the MCP until the associated fix is passed.

In a non-FMS airplane like the 747 Classic, the CLEARED altitude is usually set in the MCP, and the vertical speed adjusted to make the intervening restrictions.

I'm a fan of placing the CLEARED altitude in the MCP and monitoring performance as required for the intervening restrictions. There may be exceptions to this general rule, but I have no specific examples.
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Old 5th Mar 2007, 19:29
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Thank you for your inputs to this subject so far. At the London Terminal Control Centre we already see the Selected Flight Level (SFL) that is input into the Selected Altitude window on the MCP for all aircraft that are Enhanced Mode S capable.

This has been the case for the past 9 months or so. The controllers are using the SFL indication in the Track Data Block on the radar displays to identify potential level busts. They do this by comparing the Cleared Flight Level, as issued by the controller, with the Selected Flight Level downlinked by the aircraft. Once identified, a potential level bust can then be mitigated by an R/T dialogue. In the not-too-distant future, it is hoped to automate this checking of Cleared -vs- Selected level.

The value input into the Selected Altitude window on the MCP is already being communicated to ATC and used by controllers. Hence my query to see if there was a standard procedure regarding the value to be input when flying SIDs with step climbs. My concern is that unless there is a standard procedure to input the step climb values, as we introduce extended SIDs we shall start to see more occasions when the SFL doesn't reflect the altitude / level that the aircraft is actually climbing to, i.e. the step climb altitude / level. If we start to see these discrepancies, controllers will start to lose confidence in the SFL and may stop to use it, resulting in the safety benefits potentially being lost.
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Old 5th Mar 2007, 21:06
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Euroc5175

I can see your problem. We did our P-RNAV training on the simulator using the BEXIL 1D trial procedure. If cleared without restriction then our procedure is to set the final cleared altidude in the MCP window (2000ft at ILS 26L FAP). The five altitude constraints prior to that point would be achieved by the FMS, but Mode S would not show these.
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Old 5th Mar 2007, 21:45
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The value input into the Selected Altitude window on the MCP is already being communicated to ATC and used by controllers. Hence my query to see if there was a standard procedure regarding the value to be input when flying SIDs with step climbs. My concern is that unless there is a standard procedure to input the step climb values, as we introduce extended SIDs we shall start to see more occasions when the SFL doesn't reflect the altitude / level that the aircraft is actually climbing to, i.e. the step climb altitude / level. If we start to see these discrepancies, controllers will start to lose confidence in the SFL and may stop to use it, resulting in the safety benefits potentially being lost.
So, is there a "preference" among ATC controllers? What do they prefer to see, and why?

If there is no consensus, it is unfair to place the onus of "confidence building" on the operator and/or individual Pilot who may not even be aware his MCP is being monitored by "big brother," or what the controller "expects" to see.

After all, there are only 2 basic choices: select the "cleared to" altitude or select the next restriction. In the latter case, the controller should see a change as the airplane approaches the intervening fix. In the former case, the controller should have an "eye" for the climb rate and the speed at which the airplane is approaching the fix before he tries to use this new tool as a screening tool for perceived "cleared vs selected" discrepancies.

Is there any guidance on the controllers' use of Mode S input? If so, where can we pilots find it?
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Old 5th Mar 2007, 22:29
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Standard practice (A320) is to put the current cleared alt. in, ie. the steps, and dial in the next altitude just as you get to the restriction. BUT, if you use the kit properly to fly a SID with a step climb you would put the final altitude in the window and let the FMGS sort out the steps. The FMGS target altitude would appear on altimeter and the aircraft would climb to the next altitude once it passes the restriction. Only at the end of the SID or STAR would the target altitude be the same as what is dialled into the autopilot panel by the crew.
I sincerely hope that we will be able to fly arrivals and departures using this method shortly and not have to select the altitude manually in the autopilot all the time just because whoever designed mode S didn't understand how modern aircraft are supposed to work. Couple this with data linked ATC and my working life would get a whole lot easier and more pleasant. I think most of us (and ATC I am sure) are getting royally fed up with the state of the London TMA at the moment and a total re-think in the way it is operated is needed very soon. PRNAV and data linking cannot come soon enough, imagine climbing out of LHR heading north in blissful silence, I canít wait.
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Old 6th Mar 2007, 03:07
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Mode S

With the Eurocontrol requirement for the enhanced mode S, and the vast number of aircraft that are / will be exempt will there be enough aircraft with the "mode S display of alt preset" to have any benefit.

As to the what shall we preset, on a SID, I can see no reason (on Gulfstreams) not to set the CLEARED ALT, after all this is as well as an instruction that the A/P must respect, a memory aid, (CRM etc, etc).

On a FMS STAR, then unless the next alt or the bottom ALT is preset, the FMS will drop out of "blue" FMS V descent.


Lastly, what else does the enhanced Mode S display to ATC.....my mind boggles....

Glf
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Old 6th Mar 2007, 12:44
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Inserting steps in the ALTSEL window renders VNAV redundant.
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Old 6th Mar 2007, 15:06
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Redundancy is alive and well in MANY facets of the industry!
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Old 11th Mar 2007, 19:26
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The reason that my lot (I believe and many others) use the MCP window for the first restiction is that if you use any other mode other than VNAV (and we accelerate the aircraft after take off in TOGA mode) then the aircraft will not level at the altitude selected in the FMC, it will climb to the MCP selected altitude. Hence it introduces a chance of an altitude bust... Also, not all climbs are made using VNAV, as when we are light we would see alot of TCAS RA's simply due to the climb rate, so vertical speed mode is often used.

Now, with the MCP altitude being downlinked to the controller, could we omit (that is if the aircraft is suitably equipped) the cleared alt bit in the initial call and simply pass the current alt and the SID?
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Old 11th Mar 2007, 19:49
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Interesting discussion.
On the EMB145 we don't have VNAV as such (no jokes please) , so the only way to do a step climb/descend SID/STAR is by selecting the next constraint in the MCP and reselecting when passing the restriction point, in your example 3,000ft initially.
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