V1 for skid resistant runway

[Hardy Heinlin]

I meant adding allowed takeoff weight, flap setting, assumed temperature data, etc. (like a full-time performance engineer department).

PSX already takes gross weight (takeoff weight in the NG FMC), flaps, thrust derate, pressure altitude, OAT, slope, wind, runway condition into account. All these parameters are to be set in the FMC by the crew (or by uplink in the NG FMC). The V speeds you get in PS since version 1.0 are no fake speeds :-) PSX includes dedicated algorithms and databases (balanced field) for that.

If you don't mean the math itself but just a new graphic interface for a flight planner console -- no, PSX will not get something like that. There are already enough external programs for that job.

In PSX the math sits in the FMC, and the control sits in the CDUs. And the uplink model will use the same math. Add-ons can intercept the uplink though, and uplink different data.


|-|

[DougSnow]

Problem is that FMC-derived speeds are based on a level dry runway at sea level with a balanced field length as the V1 policy.  The FMC doesn't know about clearways and stopways (which can unbalance the field), obstacles off the departure end,  your V1 policy, if you're using alternate forward CG for takeoff, MELs requiring an adjustment to the V-speeds, if the runway is narrow or standard width (for aircraft that can do that), the list goes on.

Most airlines don't fly that way anymore. We use systems like AeroData (who I am very familiar with - I helped set up and train the TLR at my last now-defunct airline (RYN). My current carrier does this in-house - our crews currently use a performance laptop, but that will be changing soon to an ACARS solution). By using a more advanced system we can lift more weight off a runway by better optimizing the V-speeds and unbalancing the field as long as the AFM permits it. We can also use reduced and derate thrust to the fullest extent (within the limits of the AFM) by using more advanced speed systems.

Our system also knows if the runway is grooved or PFC overlay, or not (I can also set the calculation to ungrooved if there are NOTAMs saying so).  I never see if there is any real change in grooved/PFC or not for takeoff as most of the places we go runway length (outside of KSNA - 5701 ft TORA) is never a problem. But performance engineers like their numbers

None of our procedures on any of our fleets use the FMC-derived V-speeds for anything.

[Hardy Heinlin]

I guess most, if not all airlines, nowadays don't select the FMC computed V speeds on the TAKEOFF REF page. Some even use the option to hide them, as we know. I think that those that don't hide them don't select them either but just use them for comparison before entering the dispatcher's values. For this reason the NG FMC has a comparison feature that can be toggled on and off; it can display the FMC computed speeds in the center of the page and the entered values on the right side as usual. This is just for comparison.

Problem is that FMC-derived speeds are based on a level dry runway at sea level with a balanced field length as the V1 policy.  The FMC doesn't know about clearways and stopways (which can unbalance the field), obstacles off the departure end,  your V1 policy, if you're using alternate forward CG for takeoff, MELs requiring an adjustment to the V-speeds, if the runway is narrow or standard width (for aircraft that can do that), the list goes on.

It's clear that all these unbalancing parameters are not in the FMC. But I would exclude three of them: The dry/wet parameter can be added in the FMC optionally (plus "skid resistant" in the NG FMC). And the FMC does know the pressure altitude from the ADC. The slope can be entered as well.


Cheers,

|-|ardy

[richjb]

Good evening,

maybe a question for the dispatchers ...

We have a V1 for dry and a V1 for wet conditions. What V1 do we need if we have a wet "skid resistant" runway? Is it equal to the dry V1, or is it somewhere between the dry and the wet V1? The difference is very small anyway.


Regards,

|-|ardy

Hardy,

Not sure you had your question answered, so I'll take a crack at it.

The certification rules permit the OEM to furnish wet runway takeoff data for a skid resistant surface (i.e., a grooved for PFC runway surface).  The braking coefficient of friction on these surfaces is better than on a wet smooth runway surface, but not as good as on a dry skid resistant surface.  Accelerate stop distance could be shorter on a wet skid resistant surface verses a wet, smooth runway, and could result in a different (higher) V1 speed. The V1 speed will be specific to the skid resistant surface accelerate stop distance data in the AFM.

The operating rules in the US permit the operator of a turbine engine powered, transport category airplane to use data, if the OEM furnishes it in the approved performance section of the AFM (it's not "advisory data like contaminated runway data), provided the runway is designed, constructed, and maintained in manner acceptable to the FAA Administrator.  And, that's a loaded question depending on who you speak with.

Speaking with some of the Boeing performance engineering training people who I work with in industry groups, some operators are using the skid resistant performance data, while other are not.

How the data is furnished to flight crew, I believe has been answered.

Hope this helped.

Rich Boll
Wichita KS

[Hardy Heinlin]

Thank you for the good tips, Rich.


Regards,

|-|ardy

[dhob]

The NG FMC was developed for the 747-8, and then offered as a retrofit to the 744. As such, the 747-8 performance is all digital (not in the AFM) and was certified with skid resistant performance data. Thus AeroData, using the 747-8 SCAP files from Boeing, incorporate the airport runway surface condition and use skid-restraint surface data if the runway is grooved etc.
The 747-400 was never certified with skid-resistant data. Thus, this NG FMC capability is not functional on the 744, much like the Vertical RNP/ANP, or Quiet Climb.