1. Low Flying Planes

Why do planes fly so low over Great Hill? The Airport approach glide-path should never have been directed over a Hill only 1/2mile away, and then that Hill should never have been densely populated with residential homes, but concerns about that and the impact of 5-ton 9-passenger  turboprops carrying 400gallons of jet fuel are not being considered in any Airport planning. Planes landing and taking off require distance from obstacles on the ground. To ensure this, the FAA has defined trapezoidal approach and departure surfaces sloping upwards from the ends of the runway on either side of the Flight path. The width of the trapezoids vary along the flightpath and define the areas of the approach surfaces over which planes are allowed to fly. The half width of this trapezoid at the top of Great Hill based on FAA data for different types of approaches is seen in this table above 

                Runway Type                                               1/2 Width at Great Hill*                       Slope

  •  Visual, approach speed< 58 mph                                      150'                                          15:1   
  • Visual >58mph, <12,500lbs                                                350'                                           20:1 
  • Horizontal guidance >3/4                                                    500'                                           20:1 
  • Instrument visibility ≥3/4 mile                                              894'                                           20:1   
  • Vertical guidance                                                                 363'                                           30:1  
  • Instrument Departure                                                         1385'                                          40:1 
  • *Calculations based on data Tables 3.2 and 3.4 in AC 150/5300-13A

2. Houses on Great Hill

The topographic profile from the northern end of the runway over Great Hill is shown in drawing 10 in the Airport Layout Plan  submitted in June 2020. The highest ground level on the flight path is shown as 98ft above sea-level or 35 ft above the runway. However at the top of the Hill, there are higher elevations on both sides of the flight path, but still within the boundaries of the approach surface. The highest level is 133ft and the roof of the house is then at ~160ft
3. Houses at the Top of Great Hill
The picture on the left shows the ground-level heights of the many houses at the top of Great Hill. They are all on ground above the 98ft shown in drawing 10 of the Airport Layout Plan shown above. The highest is the house at 127ft, which is within the current visual approach surface. The roof will be another ~30ft higher at ~160ft. This house therefore extends ~60ft higher than the highest ground level of 98ft shown in the Airport Layout Plan drawings. No houses are shown in the these drawings either, but they show removing trees lower than the houses. This is quite ridiculous and misleading. A 30:1 slope is also included in this drawing, despite having already been rejected as “too costly” and too intrusive.
4. 40:1 Departure Surface
Similarly, drawing 12 in the Airport Layout Plan is equally misleading. In addition this drawing shows a 40:1 departure surface, which has never even been mentioned elsewhere, although it appears to be an FAA standard. It is, of course, totally impossible in Chatham as it would require 46+ avigation easements shown on the figure  These drawings do not reflect a worst case design, and the concerns of the residents of Great Hill..
5. Planes Fly Low over Great Hill

Planes are already flying extremely low over Great Hill. The standard safest glide-path slope for all airports is 20:1 (3⁰). To land at the runway threshold using this 3⁰ glide-path, the planes would have to fly at 10ft above the roofs of houses at the top of Great Hill as shown in the figure below. This is obviously not viable, but every 10ft of additional clearance over Great Hill moves the landing 200ft further down the runway An alternative is to increase the glide-path angle, but this is limited by FAA Order 8760.50. The Pilatus turboprop is allowed a maximum glide-path angle of 4.2⁰. In practice these planes appear to be using 4⁰, but these planes could still only be 100ft or less over some of the houses on Great Hill. In poor visibility with a lower minimum decision height, planes would still have to conform to the same glideslope over Great Hill as shown by the red pointer in the figure on the left. This shows an instrument approach with an Minimum Decision Height of 250ft, but the height above the house would still be 100ft. This is not adequate by day in visual conditions, but at night in poor visibility this would be even more scary to the residents than it is now. It seems counter-intuitive, that planes would not fly any lower, if a poor visibility approach were approved, but they are just too low at all times.

6. The Design Aircraft

The so-called Design Aircraft is an important aspect of airport design (AC 150/5300‐13A) and must be defined in the AMPU, since it determines the airport design standards. These include dimensional requirements on an airport, such as the size of certain areas protecting the safety of aircraft operations and passengers. AC 150/5000-17 sets the standards for choosing a design aircraft.  An accurate Design Aircraft determination matches aircraft operational area dimensions to the most demanding aircraft that regularly uses the Airport. Two key parameters of the aircraft, which are used in this determination are Aircraft Approach Category (AAC), and Airplane Design Group (ADG). AAC defines the highest approach speed (A, B, etc) and ADG the largest wing span (I,II, etc) allowed.

These parameters must match the allowed parameters of the Runway Design Code (RDC). At Chatham the Runway Design Code designated in the Airport Layout Plan as both Existing and Ultimate is B-I-5000. 5000 designates a visual approach with >5000ft visibility.  ‘B’ defines the AAC category with approach speeds <139mph, and ‘I’ the ADG category as a wing span <49ft. Hence the Beechcraft B-58, which is in the B-I category, is appropriately designated in the AMPU as the design aircraft.

However Flightaware global flight-tracking data from 2019, the last normal year of operation before COVID-19, show that there were 212 (2 per day in August) Pilatus PC-12 turboprop landings at Chatham Airport, although only 170 were recorded in the Airport log, but only 26 landings of the Beech Baron B-58 and similar B-55 combined. In AMPU §4.9.1 Gale Associates wrote that “Upon recent discussions with Airport Management, it was discovered that the Beech Baron B‐58 and aircraft with similar characteristics, remain the most demanding aircraft utilizing the Airport, and therefore, it shall remain the design aircraft.” This was clearly disingenuous, since the 9-passenger Pilatus is much larger, almost twice the maximum take-off weight, more demanding of airport standards, and an order of magnitude more frequent. Most importantly it has a 53' 3" wingspan, which is greater than 49ft, which puts it into the "II" design group, whereas the B-58 is in the "I" design group, but why was the PC-12 not chosen as the design aircraft?

AMPU §4.9.1 continues “The Chatham Airport be designed to B‐I (small airplane <12,500lbs) standards consistent with FAA Advisory AC 150/5300‐13A.” B-I was confirmed in the recent Airport Layout Plan as the Existing and Ultimate Runway Design Standard for Chatham and approved by the FAA.

The Airport design dimensions, specified in that Advisory for B-II, are not met at the Airport. Just to meet them would require clearing a 500ft width along the runway by removing ~8 acres of trees and the bike path, removing ~4 acres of trees, wetlands and vernal pool at the ends of the runway, moving the just tarmaced taxiway by 90ft, and executing 22 avigation easements at great cost to the Town and property owners.

A plane in the "II" Design Group is clearly more demanding of airport standards than one in the "I" Design Group, and the Pilatus PC-12 is an order of magnitude more frequent. It should therefore by definition be the Master Plan Design Aircraft for Chatham Airport. but that would be in violation of the existing design standards at the Airport.  Yet PC-12 planes continue to use the Airport with great frequency. This is important, because the AC 150/5300‐13A specifies that a design aircraft determines the application of airport design standards and that “Any operation of an aircraft that exceeds the design criteria of the airport may result in either an unsafe operation or a lesser safety margin”. There is presently a serious safety issue at the Airport, amplified by a short runway and people living in the RPZs.