14 CFR Part 71

[Docket No. FAA–2012–1168; Airspace

Docket No. 07–AWA–3]

Re: Proposed Modification of the Dallas/

Fort Worth Class B Airspace Area; TX

To all involved parties, 

While the reduction in Addison's class D airspace may not seem like much, it is in an area where

operations are already in a very tight fit with DFW traffic to the west, DAL traffic inbound from the

east-northeast and large amounts of corporate, fractional, cargo and training traffic underneath at ADS.

In fact, the final approach fix (JERIT) for ADS Rwy 15 is at 2000 MSL, which would leave only 500

feet separation between IFR arrivals into ADS and DAL traffic at 2500 if this airspace change goes

through (border of Area F and Area H). 

There are numerous ways to avoid having to redesign the existing airspace. Although I'm sure others

will suggest vectoring airliners further to the north and west before their southbound turn towards

DAL, this is not efficient with respect to the jets. Anything that increases fuel consumption for the

airlines is not only irresponsible environmentally, but financially. Likewise, the hundreds of small

businesses that rely on ADS should not be marginalized in the effort to reduce the impact to airliners. I

am not writing this from the standpoint of "big airliners are against little piston planes". Instead, I am

writing this as the result of several years of observing and studying airspace and testing new methods

of utilizing the existing structures. After reading the NPRM on the changes to DFW's airspace, it is

apparent that we are not fully utilizing the full capabilities of modern jet airliners. 

The upside-down wedding cake design of Class B airspace is optimized for steep climbs and descents.

Standard Class B has a floor gradient of 300 ft/nm out to the 10nm ring. This equates to only 1000fpm

at 200ktas or 1250fpm at 250ktas. But again, this is for purposes of containing traffic inside the

airspace, not a limitation on using higher gradients. With the advent of RNAV STARs, GPS

approaches, and the upcoming NextGen system, creating 3D highways in the sky is no longer a fantasy

but an easily employable system that works in VFR or IFR conditions. The only way to fit more aircraft

into the volume of airspace such as that around DFW is to increase the angle of descent at critical

segments inside the Class B.

For separation and flow purposes, many congested terminal areas drop arrivals down 30 or 40nm out so

that departures can climb unobstructed above them. This is because in areas like the DFW Class B, the

proximity of DFW, DAL, ADS, AFW, NFW, FTW, GKY, GPM and RBD makes it very hard to get

everyone where they need to be at the same time. When most of the non-RNAV STARs were designed,

it was hard to conceptualize how to position aircraft three-dimensionally. Now that most airliners and

many corporate aircraft feature VNAV, FPA symbology and the ability to climb or descend in excess of

2000fpm, being able to follow a constant descent path is much easier to plan and execute. 

As mentioned before, the standard floor gradient for Class B is 300ft/nm. Modern jet aircraft can climb

at more than twice this rate under most conditions. Descending can done at even faster rates thanks to

speedbrakes and high flap extension speeds in most jets. If the airplanes are capable of flying steeper

flight path angles in the terminal area, why aren't they currently doing so? The most common reason I

heard from talking to other pilots and researching airline procedures was that jets needed to configure
early for landing. While this may be true to an extent, there is no commercial aircraft that needs 40nm

to configure for landing. Others said that excessive descent rates near the ground could lead to terrain

avoidance issues. This would be true if an aircraft was at 200AGL, unstabilized and on a very steep

approach path. But again, a descent rate isn't always an issue, it is also the angle (a 3.0 degree

glidepath at 300 knots ground speed has the same descent rate as a 7.5 degree glidepath at 120 knots

ground speed). In any case, a testable profile was needed before going further. 

The solution seemed to be one of creating an extension of the Optimized Profile Descent for the closein terminal area. Testing this theory in various FTDs, talking to pilots of different aircraft and flying the

procedure in real aircraft has shown that an average glide angle of 6 degrees results in a power-off

approach with no increase in airspeed (in reality the range was roughly 4.5 to 7.0). Depending on

configuration, very low levels of power may be required to maintain airspeed. This power setting will

invariably be less than that used during the current step-down method of approaching. This has

tremendous advantages for noise abatement, fuel conservation, reduced carbon emissions, airspace

utilization and wake turbulence avoidance. Workload can be reduced by the use of the IAS function on

the autopilot to ensure that ATC assigned speeds are adhered to. 

By flying an average 6 degree descent angle, aircraft are no longer forced to fly shallow paths to the

target airport. This opens up vast parcels of airspace that previously were underutilized. At 200 knots, a

jet flying a 6 degree path will be descending at 2200fpm, obviously about twice the normal descent rate

for that airspeed. Since jets are not as responsive as light GA airplanes in the approach phase, a 6

degree glide path has to convert to a standard 3 degree glide path at some pre-determined distance from

the runway, most likely 1500 to 1000 AGL and 1.0nm prior to passing the FAF (depending on the

aircraft type and wind conditions). 

Further out in the Class B airspace descent angles can be more conventional if satellite airport conflicts

are not present, allowing jets to "pre-configure". This includes possibly going to a minimal flap setting

that would produce enough drag to keep speed from increasing in the steeper descent to come. Some

aircraft that are extremely clean with high inertia such as the A330 and B777 may require shallower

angles or the use of speedbrakes if airspace cannot accommodate a flatter approach. Like any air traffic

management procedure, flexibility will be required when dealing with various aircraft types. 

Using this type of approach in the northeast sector of the DFW Class B would bring Love arrivals over

Addison between 3000 and 4500 MSL (depending on where they are being vectored from). This is a

substantial increase in the current safety margin for both Addison and Love arrivals. An additional

benefit is that Love's lateral spacing would not have to be modified from what exists today, reducing

the potential for conflict with Dallas/Fort Worth traffic on the Cedar Creek Six arrival when a south

flow is in use. Around the DFW Class B, departures leave the terminal area on north, east, south and

west headings, while arrivals enter on northeast, southeast, southwest and northwest headings. This

existing deconfliction works well with 6 degree descent angle as departures would not risk losing

separation with arrivals.

The whole idea behind the 6 degree approach is to use what we already have freely available without

making any particular group of operators have to suffer. If employed properly, the procedure would

actually save money for both commercial and general aviation operators. After proving its worth in

solving this conflict, the procedure can easily be implemented nationwide for reasons as varied as

traffic management, delay mitigation, noise abatement and reduced emissions. I sincerely hope that the

FAA studies this solution further as it would ensure the spirit of cooperation that made American

aviation great is still alive and well in this country. 
Sincerely,

Christopher L. Williams

ASEL, AGI

chris@semperapollo.com

972-310-8114
Supplement:

A: Example of a 6 degree approach for DAL runway 13L.

Cross WADES at 7500 MSL, 

1.0nm prior to NITER, maintain 1900MSL and intercept ILS or conduct visual approach once

crossing the FAF. 

B: Conversion to 6 deg approach.

If one wishes to convert any approach to a 6 degree variant, simply decide what the conversion altitude

or intersection is (when or where the approach changes from 6 to 3 degrees) and how far back from

that point the approach will commence. Applying basic trigonometry will provide the IF crossing

altitude. For example for DFW's runway 17L:

FAF = GBUSH, 2300MSL 

IF = RIVET, Unknown MSL, 12.6nm from FAF

sin descent angle x distance to FAF x nautical mile in feet + FAF altitude 

((sin6 x 12.6) x 6076)) + 2300 = 10302 MSL at RIVET