Every now and then, setting up for landing on a wet, short runway, I hear that we should consider the grooved runway to be dry.
I have flown aircraft that allow this, but the Gulfstream does not in the case of the G450. (They do on the G150.) There isn't a lot of current research out there, most of it was done forty years ago. Aircraft manufacturers can take advantage of grooved runways in performance numbers if they wish, but they don't have to.
We all know intuitively that a grooved runway makes it easier to stop. But braking on a wet, grooved runway as easy as on a dry runway? No, but it is more complicated than that:
Given that, I wonder if my previous aircraft manufacturer was giving us too much leeway to consider a wet, grooved runway to be dry for takeoff and landing. The key takeaway: if the grooved runway is wet with less than 0.1" depth, your takeoff performance is nearly as if the runway was dry. Your landing distance is improved, but not as dramatically. You still need to plan according to the manufacturer's performance charts, but know you may do better in actual practice.
Everything here is from the references shown below, with a few comments in an alternate color.
[AC 150/5200-30D, ¶4.71] Pavement Surface Modification. Surface texture and surface treatment modifications by themselves will not increase the coefficient of friction of ice formed on the surface, but both will enhance the response of chemical treatment.
That tells us grooving works. But how well?
Figure: Test aircraft, from Pavement Grooving and Traction Studies, page 121, figure 2.
The NASA Langley Research Center conducted tests to determine the affects of grooved runways on aircraft braking performance at the NASA Wallops Station in 1968. Flight tests were conducted using an Air Force F-4D aircraft and a NASA Convair 990 aircraft. The results were presented in a conference report that compiled 27 papers from this and other studies. It is dry and convoluted writing, 521 pages of it, but there is a lot to be gained from selective reading. A copy of the report is linked, and excepts follow.
These tests were conducted in 1967. The FAA updated these tests in 1983, which fine tuned and corroborated the earlier findings. You can read about these tests in a presentation made in 2011: Daiutulo, which you can download below.
While the study covered various topics, such as tire wear and runway drainage, only three of its focus areas are of interest to us here:
Figure: Effect of slush covered runway grooves on directional control of 990 aircraft, from Pavement Grooving and Traction Studies, page 63, figure 24.
Figure: Effect of runway wetness condition and surface configuration, from Pavement Grooving and Traction Studies, page 49, figure 2.
Figure: Cornering force, from Pavement Grooving and Traction Studies, pages 50 - 53, figure 3.
A grooved runway gives you a definite advantage on takeoff in either the stop or go scenario. If the takeoff is continued, this so-called cornering ability helps keep you within centerline tolerances.
More about this: VMCG - Minimum Control Speed Ground.
Figure: Braking effectiveness, from Pavement Grooving and Traction Studies, page 52, figure 4.
Figure: Landing field lengths, from Pavement Grooving and Traction Studies, pages 109 and 110, figures 2 and 3.
Figure: Balanced field lengths, from Pavement Grooving and Traction Studies, pages 111 and 112, figures 6 and 7.
Figure: Balanced field lengths on slush, from Pavement Grooving and Traction Studies, page 113, figure 10.
The Feds give you the option of factoring in grooved runways, but not all manufacturers do. In fact, some manufacturers have different rules for different aircraft.
[14 CFR 25 §25.105(c)(1)(ii)] The takeoff data must be based on . . . At the option of the applicant, grooved or porous friction course wet, hard-surfaced runways.
[14 CFR 25 §25.109(d)] Accelerate-stop distance. . . . At the option of the applicant, a higher wet runway braking coefficient of friction may be used for runway surfaces that have been grooved or treated with a porous friction course material.
[14 CFR 25 §25.1533(3)] Additionally, at the option of the applicant, wet runway takeoff distances may be established for runway surfaces that have been grooved or treated with a porous friction course, and may be approved for use on runways where such surfaces have been designed constructed, and maintained in a manner acceptable to the Administrator.
I've flown aircraft that allowed pilots to consider wet grooved runways to be essentially dry. The Gulfstream G450 does not. The performance section of that AFM does not mention runway grooves at all. The only thing in our books on the subject appears in G450-OIS-02:
[G450-OIS-02, page 19] For landing operations on a wet, grooved runway, data in this OIS will be conservative.
This leads me to believe Gulfstream has not factored in grooved runways and wants you to use it as a safety pad. Interestingly, the rules for the G150 do allow the consideration of grooved runways.
More about this: Braking Action.
14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation
Advisory Circular 150/5200-30D, Airport Field Condition Assessments and Winter Operations Safety, 3/8/2017, U.S. Department of Transportation
Daiutolo, Hector, The Benefit of Runway Grooving, FAA/Asphalt Institute Airport Pavement Workshop, October 18-20, 2011.
Gulfstream G450 Operational Information Supplement, G450-OIS-02, Contaminated Runway Performance, Revision 1, August 3, 2011
NASA SP-5073, Pavement Grooving and Traction Studies, 1969
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