Pilot Reported Roughness: Roughness Investigation and Repair
By: Kevin Chee of the Greater Toronto Airport Authority
Michael Gerardi of APR Consultants
Pilot Reported Roughness
Figure 1. This plot shows us the profile of the runway before the 2011 overlay (top) verses the profile after the 2011 overlay (bottom). After completion of the 2011 overlay, long-haul 777-200 aircraft were experiencing unacceptable aircraft response when traversing the intersection of Runway 15R. As seen in this plot, the crown of Runway 15R is quite different than it was before the 2011 overlay.
Figure 2. This aircraft simulation plot depicts the aircraft response predicted when a Boeing 777-200 encounters the intersection area after the 2011 overlay. As you can see, both the Pilot’s Station Acceleration (upper band) and the Aircraft’s Center of Gravity (middle band) experience poor aircraft response when encountering the intersection of Runway 15R. What APR and GTAA learned in this project is that the intersection of 15R did not cause the poor response by itself. Multiple Event Roughness before and after the intersection coupled with the crown of the intersection led to the poor ride quality experienced by this and similar aircraft.
MEASURING THE PROFILE - DEFINING THE PROBLEM
A traditional survey crew measured the affected area of the runway. APR used that profile data to conduct a variety of takeoff and constant speed taxi simulations to help pin-point the roughness events. Because the intersection of 15R is located near the midpoint of 05-23, this roughness will affect takeoff operations in both runway directions, 05 and 23. What APR’s analysis found is that the aircraft did not respond to just one event, the intersection with 15R, but was responding to a series of events that led up to the 15R intersection. The bumps and dips preceding the intersection caused the aircraft to “rebound” from those events as it encountered the up-side of the 15R intersection. Figure 2 illustrates the measured profile of the affected area as measured in 2007 (top) and the new profile, measured after the 2011 overlay. Note the difference in pavement profile located around the 1,540-meter mark.
Figure 3. Here, the “as-is” profile after the 2011 overlay was completed can be seen in the upper portion of the plot. After reviewing numerous repair scenarios, the profile in the lower half of the profile was the advice APR provided to the GTAA to obtain improved aircraft ride quality.
Figure 4. When simulating the same conditions using the 777-200 model on the analytically repaired profile, the ride quality of this area improved significantly. There are no areas where the aircraft’s accelerations are predicted to exceed the red +/- .40g threshold of acceptability.
OPTIMIZING THE REPAIR
Once the bump locations were identified, APR began an iterative process of making straight line repairs to the measured profile. This process involved making conservative modifications (analytically) to the profile, then simulate an operation, in this case, a high-speed taxi using a model of a Boeing 777-200. This process is repeated until the desired ride quality is achieved. Figure 3 illustrates the notional changes to the runway’s profile (bottom of plot) versus the original profile (top). Once the optimum repair was designed, the repair profile was provided to the GTAA for use by their paving contractor. APR’s simulations indicate that the repaired profile yields a dramatic improvement in ride quality for the 777 aircraft. As Figure 4 shows, the aircraft’s accelerations are well within the .40g threshold of acceptability.
Figure 5. This plot shows the original 2011 overlay profile (top) with the APR engineered repair advice provided to the GTAA (middle) followed by the final, post repair profile existing at the airport today (bottom). As you can see, the actual repair is similar to the engineered repair provided by APR.
Figure 6. Here is an aircraft simulation repeating the same conditions as the previous simulations, only on the newly repaired profile. As you can see, the aircraft response is much better through the majority of the repair. What is important is that the dynamic loading created by the areas of roughness are less, which should translate into longer pavement life for this section of pavement. Also, the pilot complaints have ceased when operating from this runway.
VALIDATING THE REPAIR
Later in 2014, APR was asked to re-assess Runway 05-23 to update the pavement management program at YYZ. Using the Auto Rod and Level, three lines of survey were measured of this runway. Figure 5 plots the post repair profile of the affected area compared to the original problematic profile and the analytical repair APR provided to the GTAA. When assessing the ride quality of the actual repair, the ride quality was improved significantly, eliminating pilot complaints (Figure 6).
It makes sense to evaluate a runway design anytime an intersection is involved, or if it is necessary to tie into existing elevations with vertical curves. It is a cost-effective method to ensure that the intended profile does not create a ride quality problem. This analysis could prevent unnecessary corrective action and added expense.
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