Wet Runway Landing Data NOT FAA Approved?

aviategw

Well-Known Member
Why is the wet runway landing data in my CE-680 AFM, and by extension CessNav landing calculations, not FAA approved? Cessna specifically states that the wet landing data is advisory only and not FAA approved. Is there an official sounding explanation anywhere as to why that is?

Thanks in advance....
 
By FAA rules, there is no requirement to have wet runway performance data for certification (either in part 25 or 135). The only(?) required number I am aware of is the Required Landing Distance from FAR 25.125 and invoked in 135.385 for turbojets. So if the performance data does not have to be maintained as part of the certification, I guess the thinking is to avoid the cost and dogma of that status and keep it as "advisory" as an "Operational Landing Distance."

There are certification requirements for wet runway data for takeoff affecting the accelerate-stop distance.

The most I found in the FARs §135.363(f):
The performance data in the Airplane Flight Manual applies in determining compliance with §§135.365 through 135.387 [takeoff, en-route, and landing limitations for different equipment]. Where conditions are different from those on which the performance data is based, compliance is determined by interpolation or by computing the effects of change in the specific variables, if the results of the interpolation or computations are substantially as accurate as the results of direct tests.

Order 8900.1 Vol. 4 Ch 3 Sec 1 expands on the subject (my emphasis):
Performance Limits. Part 121 subpart I and part 135 subpart I require operators conducting air transportation operations to conduct those operations within specified performance limits. Operators must use Federal Aviation Administration (FAA)-approved data to show compliance with these regulations, supplemented as necessary with manufacturers’ advisory data, for wet and contaminated operations. The aircraft certification rules require the manufacturer to determine the aircraft’s performance capabilities at each weight, altitude, and ambient temperature within the operational limits. The performance section of the AFM or RFM presents variable data in tabular or graphic format. Operators must use data extracted from the performance data section of the AFM or RFM to show compliance with the operating rules of part 121 or part 135. For those aircraft certified without an approved flight manual, the FAA-approved data may be placed on placards or placed in an approved CFM.

Required Landing Distance. The required landing distance is established during certification and is the distance needed to completely stop from 50 feet above the runway threshold (i.e., the point at which the obstacle clearance plane intersects the runway. In establishing landing performance data, the airplane must approach in a steady glide (or rate of descent) down to 50 feet at speed not less than VREF for the chosen landing flap setting.

Operational Landing Distance. These distances are advisory performance data (i.e., not required by regulation) which are intended to provide a more accurate assessment of actual landing distance at time of arrival, considering factors which cannot be accurately predicted at time of dispatch, such as runway contaminants, winds, speed additives, and touchdown points. These distances may be based upon the use of reverse thrust, ground spoilers, autobrakes, etc.

My read is that the Required Landing Distance is calculated on an idealized runway (FAR 25.125 does not mention wet/contamination or gradient)
 
Because they don’t make runways that long, and it’d look bad for marketing? :smoke:

Beech did the same thing with the King Air 200. They published Accel Stop/Go tables when they’re not regulatory. It’s nice to know, though. So, since all pilots nowadays have to be lawyers, too, look at it this way:
“So Captain Over, the manufacturer provided data which proved the runways wasn’t sufficient, yet you proceeded?”
“The data wasn’t approved.”
“But did that manufacture’s data indicate the runway was long enough?”

Who’s going to win that one?
 
How about the FAA require manufactures to publish the following data in flight test:

wet (in case it rains)
Snow (in case of winter)
Ice ( in case of fools)

Awacs
 
The problem with data that is “required” or “approved” can come in defining the conditions involved, and then finding/duplicating those exact conditions to actually perform the tests needed.

Much easier (arguably) to use “advisory” data which can be put together in a looser fashion, but still gives operators some useful information in making judgements.
 
How about the FAA require manufactures to publish the following data in flight test:

wet (in case it rains)
Snow (in case of winter)
Ice ( in case of fools)

Awacs

just spitballing here, but possibly because “wet” “snowy” and “ice” have tons have variables. Things like standing water (puddles) or dry snow vs wet snow vs slush etc.
 
To further confuse the issue...

After some overrun accidents the FAA published some Advisory Circulars. These AC's dealt with landing data, breaking action and efforts to use a common method of runway contamination reporting and corresponding breaking action reporting and prediction. AC25-32 Landing Performance 12-22-15

11.3 Contaminated runway landing performance data approved by either the Joint Aviation Authorities or EASA in compliance with either their contaminated runway type certification or operating requirements are acceptable when using the optional process identified in this AC, with the following caveats:

11.3.1 The data provider should develop data that accounts for all of the runway surface condition descriptions identified in table 2 of this AC (unless operating limitations prohibit operations on runway surface conditions for which data are not provided)
.

Some of the specifics of runway conditions may not have originally been part of the aircraft certification basis. I went to FSI on the Beechjet and the runway data for that airframe in the higher contamination amounts were not FAA approved. Raytheon was not about to do testing for an aircraft that is no longer being manufactured. Specific contamination values now required in part 121 were not required for original aircraft certification.
 
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