Assessment of runway braking action

[PEI_3721]

From another forum:-
The most recent FAA documents (six) on TALPA and avoiding an overrun, @
http://www.skybrary.aero/bookshelf/content/index.php?summarySearch=&categorySearch=&authorSearch=&titleSearch=&dateSort=desc

The revised AC150 5200 Airport Field Condition Assessment has two similar TALPA Matrix. One is for Airport Operator Use (page 67), and the other is for Pilot Use (page 68) for relating the runway condition to a braking action.
The first allows use of a ground vehicle to provide an assessment; the second relies on pilot assessment - PIREP.
How can these subjective assessments be equivalent, i.e. provide a consistent report, is 'a noticeable reduction in braking' in an unspecified vehicle the same as 'a noticeable effect' in an aircraft. If not then the ground assessment of braking action could differ significantly from the reality experienced by a crew.

It would appear that the more reliable estimate of braking action is to use the contaminant type and depth.
Is this a valid concern, if not then why not.

[Intruder]

What is better: A single report from a vehicle with unknown tires and brakes, or a PIREP by an airplane of a type known to you? How can YOU translate a contaminant type & depth to a braking assessment for YOUR airplane?

Though I fly the 744, I suspect that many heavy/large (and even smaller) transport airplane types with antiskid systems behave similarly. Whether or not a particular pilot on a particular type may have the "feel" of the brakes is yet another question. Still, I can feel when the antiskid system releases the brakes, whether using autobrakes or manual braking. I can do a subjective assessment of how often and for how long the antiskid releases the brakes, also knowing the level of effort (autobrake setting or foot pressure). The more the antiskid has to work, and the more I have to compensate with rudder for asymmetry, the worse the condition is. In a nutshell:

No antiskid releases, or infrequent, short antiskid releases: Good

Noticeable, but controlled, antiskid releases: Medium/Fair

Frequent, prolonged antiskid releases and/or large asymmetric releases: Poor.

For those without antiskid systems, translate those releases to the requirement to manually release or moderate brake pressure to a degree less than otherwise desired.

In any case, such a PIREP system translates to a performance level that another pilot can relate to, even if not "exact" for his airplane type. After all, NO performance calculation on a contaminated runway can ever be "exact".

[safetypee]

The particular columns of the RCAM are only used to downgrade the braking action.
If a vehicle reports an erroneous improved conditions then because this does not change the reported braking action then the landing risk is unchanged. But if the vehicle fails to identify deteriorating conditions, then the risk increases; this is important for those operators who use reported runway condition as the basis of landing performance (Boeing ?).

I cannot see how a vehicle assessment can be related to an aircraft. 'Mu' measurements use similar tyre technology and have been shown to have little correlation with aircraft performance.
Vehicle tyres and brakes are very different to those on an aircraft. Is it a small vehicle or a large off-road AFRS; - what tread depth, deep grooved winter tyres or not, ABS vs AntiSkid.
Driver experience and judgement may not equate to a pilot; is the driver a pilot, is experience of direction control limited to road widths, if so then runways might appear less restrictive.

What might seem like a good idea could introduce an additional, subjective hazard in already difficult operations

[PEI_3721]

Intruder, there is little safety benefit in choosing between two subjective and possibly misleading sources of information.
AFAIR Airbus landing data is based on contaminant type and depth.

Your subjective 'anti-skid' assessment is a personal choice which has little in common with the descriptions in the TALPA matrix. Thus your PIREP may be another 'meaningless' source of information - you know what it means, others might not. Is that a help or hindrance for safety.
The implication that a PIREP can be used to determine landing performance is frightening; using assessments from different aircraft types, without knowledge of reverser or brake use, landing speed, weight, or the reporters' experience ... ... hazardous

As I interpret the TALPA information, PIREPS are not to be used to determine runway braking action; the initial process requires a ground based assessment based on contaminant type, depth, and extent of runway covered. The new proposal of using vehicle assessments to revise (downgrade) the braking action appears to be of limited use and could be misleading.

If the FAA think that PIREPS have a use in down grading, then ok, but don't rebroadcast them with the risk of misleading pilots or giving false confidence about the conditions; see LGA MD 88 accident, http://www.pprune.org/rumours-news/584445-ntsb-says-delta-pilot-error.html .

[Intruder]

In the US, at least, we are often asked by the tower for a braking assessment after landing. Very often I hear that same assessment broadcast by the tower to following aircraft.

I do NOT "rebroadcast" PIREPs. That is not my job, and I have plenty to do on approach and landing. AC 150/5200-30D (pp. 5-15 through 5-20) tells the airport operators how to incorporate PIREP data into their RwyCCs.

The RCAM matrix in AC 150/5200-30D (p. 5-7) shows a very close correlation between the Runway Condition Codes and pilot reported braking action. With allowance for translation from tech-speak to cockpit perceptions, the "Pilot Reported Braking Action" descriptions are very close to what I posted above.