bee_notes

Bee, Bird and Mustang

Turkey vultures in El Dorado Hills

The Sacramento Bee said General Aviation and birds can't mix at Mustang Airport, the Audubon Society concurred. They were correct that Mustang is in an area that hosts a lot of birds, but they neglected factors that are far more important in producing risk of bird strikes. The issue of their concern has recorded only one reported bird strike in 20 years in the area within 15 miles of Mustang Airport. This area contains two public-use General Aviation airports, one of which is expected to close soon.

Here's what they missed.

Collision rates depend not only on the number of birds and aircraft in the same airspace. Two factors that can be verified from actual statistics are:l

Collision cross-section. This term is informally borrowed from its definition in particle physics. In consideration of collisions between relatively small birds and relatively larger aircraft, it is reasonable to think of collision cross section as the frontal area of the aircraft.
Speed of the aircraft. Humans and birds both use a "see and avoid" principle to stay clear of mid-air collisions. The faster an aircraft flies, the less opportunity there is for either the bird or the human pilot to see and avoid the other.

Without going into math, this one illustration gives a sense of the collision cross section for two types of aircraft: A Cessna 182, a fairly typical single-engine piston-powered light General Aviation Aircraft; and an Airbus A300-600, a wide-body airliner. Both types can be found daily in the Sacramento-region airspace. Wingspan is 36 feet for the Cessna, 147 feet for the Airbus. Bird wingspreads range from a few inches to about 4 feet for most hawks, 6 feet for turkey vultures, 7 feet for sandhill cranes, 9 feet for California condors. (Condors are not present in our area). The Cessna's fuselage width is a fair match for the wingspread of our largest hawks.

Frontal area comparison, A300-600 and Cessna 182

The bottom line is in statistics that the FAA has kept a database of wildlife strike reports since 1990. Most but not all are for bird strikes; Sacramento International has reported coyote and black-tailed jack rabbit strikes.

In 20 years only one bird strike has been reported from the airports in the south Sacramento County area that includes Mustang, and that bird strike was at Franklin Field. The opposite extreme as of April 8, 2010 is 1,453 bird strikes plus 6 terrestrial animal strikes at Sacramento International.

Comparison of risk factors and actual number of bird (or animal) strike reports in 20 years leads to a conclusion that type of aircraft is the most important risk factor. Air carrier aircraft (airliners) have a large collision cross-section and operate at high speeds. Light General Aviation aircraft have a much smaller collision cross-section and operate at much lower speeds.

Airport	Reported Bird Strikes, 20 years	Plausible Factors for bird strike risk
		Main Users		Filed Airport Traffic	Observed Airport Traffic	Based Aircraft	Bird Population	Riparian Habitat Vicinity
		Light GA Aircraft	Air Carrier Aircraft	Filed Airport Traffic	Observed Airport Traffic	Based Aircraft	Bird Population	Riparian Habitat Vicinity
Mustang	0	X		--	L	L	H	H
Sunset Sky Ranch	0	X		M	L	M	M	H
Franklin Field	1	X		M	M	L	H	H
Cameron Airpark	0	X		M	L	M	M	M
Mather	61	X	X	H	M	M	M	H
Sac Executive	29	X		H	M	H	M?	L
Sac International	1,637		X	H	H	L	H	Hs

Notes:

The ratio of birds strikes to operations is about 25 times higher at Sacramento International (SMF) than at Sacramento Executive (SAC), with both airports reporting approximately the same number of daily operations. This strongly consistent with a conjecture that the type of aircraft (air carrier or light General Aviation) is the most significant factor contributing to bird strike risk. This also tends to be support by results from airports in other areas, such as the comparison between San Francisco International (SFO) and San Carlos (SQL), where bird habitat is more similar than in the SMF/SAC comparison.
One operation is either one takeoff or one landing.
Bird & wildlife strike counts were checked in March, using the Feb. 11, 2010 copy of the http://wildlife-mitigation.tc.faa.gov/wildlife/.
L, M, and H mean Low, Moderate, and High.
For the airport daily traffic and based aircraft counts, L means 0-10; M means 11-100; H means more than 100.
"Filed" airport traffic is based on the annual reports made to the FAA by public use airports.
"Observed airport traffic is based on manually counting operations recorded by a web-based flight tracking application for one day. The day was the first Saturday with good weather in March, 2010.These conditions produced about 4 times more traffic than was seen during weather in the preceding period, when most days had marginal VFR conditions.
Actual "Observed" traffic was much lower than "Filed" traffic estimates at all privately owned / public use airports.

The content below this point was an earlier open letter to the Sacramento Bee.

In fairness to the Bee, this newspaper usually does better at assessing all salient factors for public issues than it did in this case before issuing an editorial opinion. This may be due to Bee editorial staff having limited aviation-related knowledge, it probably also involves need to work under deadlines with a much smaller staff than in earlier years.

A key point of perspective is that the Bee's opposition to Mustang was based on bird strike risk in an area with a recorded history of one bird strike in 20 years. Consideration of such very low probability events should also include events such as area flooding from the Sacramento and Cosumnes rivers. Franklin Field is in the flood plain and could be underwater in a serious flood. In that event Mustang could be the only public use airport in the area to allow air access for emergency relief. An actual case worth noting was the General Aviation airlift between Reid-Hillview and Watsonville after the Loma Prieta earthquake. That airlift, using mainly light General Aviation airplanes, carried more than 100 tons of emergency supplies while the roads to the epicenter area were closed.

Since the Bee's editorial was published there have been two significant developments:

A California Supreme Court decision reversed a number of findings of an appellate court decision. The result is that Sunset Sky Ranch (Elk Grove) has lost its Conditional Use Permit and is expected to close when Sacramento County Code Enforcement takes action.
Sacramento County approved the Conditional Use Permit to convert Mustang Airport from private use to public use. Mustang probably will absorb many if not most of the aircraft still based at Sunset Sky Ranch.

This is an open letter to the Sacramento Bee editorial board,
starting with a map-graphic preface

Turkey vultures in El Dorado Hills --

Maps: Click on any map to see a higher resolution image

Mustang and Franklin Field airport locations relative to Cosumnes River Preserve and Stone Lakes National Wildlife Refuge	Mustang Airport location relative to northeast end of Cosumnes River Preserve	Aerial view of Mustang Airport vicinity

Note on bird strike risks: The FAA database of reported wildlife strikes has recorded precisely one bird strike at Franklin Field since the database was started in 1990. The national database shows that 88% of bird strikes have no effect on aircraft flight.

Swainson's Hawk nesting sites near Mustang Airport and Franklin Field	Sandhill Crane roosting and foraging areas near Mustang Airport and Franklin Field

This questions below for the Sacramento Bee editorial staff and the notes below refer to fact-checking on the Bee's February 25, 2010 editorial about the proposed changes at Mustang airport in the editorial titled "Planes and birds can't mix safely".

Question 1: Who or what is the source of the Bee's statement that "The Sacramento County Airport System estimates a conservative low range of 15,200 flights a year or about 40 a day at the proposed new public airport."?
Question 2: What is the source of the Bee's citation of 2 flights per week as a current or possibly old number? This is much different from other reports.
Question 3: What is the source of the Bee's statistics for Oakdale Airport? They differ substantially from current FAA statistics.

---- So far I've been unable to find these citations in any source except the Bee's editorial. At a minimum the 15,200 flights per year citation is more than a factor of 2 higher than values from the EIR and the 2 flights per week citation is more than a factor of 10 less than the citations from other sources of current Mustang operations.

Here's how the various traffic citations compare, including one for current traffic at Franklin Field. Text highlighted in red boldface is cited explicitly in primary source documents, the other black unhighlighted numbers are derived from the primary citation.

	Mean Operations per Day	Mean Flights per Day	Operations per Year	Flights per Year
Mustang current traffic, Bee citation: 2 flights/week	0.6	0.3	209	104
Current rate, EIR & other planning documents	6	3	2,190	1,095
Lower bound quoted by Bee, citing an unknown SCAS source	83	42	30,400	15,200
Phase 1 daily rate, EIR and multiple other sources	13	7	9,600	4,800
Phase 2 daily rate, EIR and multiple other sources	20	10	14,400	7,200
Other airports for comparison
Franklin Field (2007) -- 10 based aircraft	99	49.5	36,135 (36,000 for 2005-2007)	18,068
Cameron Airpark (2005) -- 95 based aircraft compare with Bee citation for Oakdale	99	49.5	36,135	18,068
Oakdale Airport, according to Bee -- 96 based aircraft	99	49	36,000	18,000
Oakdale Airport, according to FAA -- 57 based aircraft	26	13	9,490	4,745

Apparent error #1: The Bee's citations of traffic at Mustang before and after the proposed project appear to be in error by roughly a factor of 2 for projected traffic after Phase 2 of the project and by a factor of 10 for current or earlier traffic.
Apparent error #2: The Bee's statistics for Oakdale appear to be very substantially wrong. Their numeric values, including the count of based aircraft, look like a remarkably good match for Cameron Airpark, in Cameron Park.
Definite error #3: The Bee said "A hardly used runway at Mustang Airport, surrounded on three sides by the [Cosumnes River] preserve". Mustang's runway is not surrounded on 3 sides by the Preserve: As shown in the maps below and as noted in the EIR and planning documents, the Preserve borders only the north and west edges of the airport.
Definite error #4: The Bee said "The expanded airport would have a wider, longer runway". The project retains the same runway length as at present. Extension of its west end by 800 feet makes up for a corresponding displacement of its east end by 800 feet.
Definite error #5, but slightly subjective: The Bee said "Can tens of thousands of birds co-exist with this many flights? Hardly." This already occurs at Franklin Field, whose location is very close to both the Cosumnes River Preserve and the Stone Lakes National Wildlife Refuge. In the Mustang EIR, maps reproduced below show a somewhat higher exposure to Swainson's hawk nesting sites and to sandhill crane roosting and foraging sites.

However, since the FAA began keeping a database of wildlife strike reports in 1990 its 20 years of data show precisely one bird strike reported for Franklin Field (2005). Additional FAA notes in a document summarizing the first 19 years of results found that 88% of bird strikes had no effect on flight of the aircraft involved. The most common source of damage due to bird strikes that requires measures such as an engine shutdown or a precautionary landing is ingestion of birds by jet engines. (Mustang will not serve jets.)

A few other notes from the FAA data at least make entertaining reading. One example is that the database records a modest number of reptile strikes, for reptiles weighing more than 2.2 pounds (1 kilogram). Among wildlife strikes resulting in actual injuries, deer are the third most frequently involved class of animals, behind two classes of birds. The database shows a fair number of bird strikes occurring on the ground, when an aircraft is taxiing, and a small number of bird strikes occurring when the aircraft is parked. Beyond FAA notes, my own house in El Dorado Hills has sustained 4 known bird strikes to its windows in 19 years. My personal experience includes a total of 3 bird strikes while driving, none yet while flying.
Point of omission: The Bee said "A new public airport is unnecessary. Adequate alternatives exist – such as Executive Airport, less than 20 miles away, or Franklin Field, 6.5 miles west."

The Sacramento County Airport System (SCAS) Master Plan and associated working papers point out desirability of routing growth to two other airports in the region instead of expanding Franklin Field facilities. It identifies a major issue for permanent development at Franklin Field being need to raise permanent structures 1.5 feet to comply with federal regulations because the field is slightly below Base Flood Elevation. It also notes that development at Franklin Field could be in cross purposes with habitat conservation efforts. The Master Plan identifies the other airports in appropriate for expansion instead as Mustang and (if still open) Sunset Sky Ranch.

Use of Sac Exec by residents of Elk Grove and Galt is possible but less desirable. Distance from Galt to Sac Exec is about 25 to 30 miles, depending on route. Distance from either Galt or the south end of Elk Grove to Mustang is about 4 miles. Benefits of shorter commutes include not only convenience for pilots, but also reductions in fuel consumption and emissions of carbon and pollutants. Principles of urban planning that emphasize compact growth tend to favor geographically distributing a relatively larger number of smaller airports instead of relying on fewer larger airports.

In checking facts my opinion of the biggest reason for not going forward is the mass of unwarranted fear-based conditions being placed on the project. If I were the field's owner I'd abandon the project because of a mass of legal hoops to jump through, leaving the same hoops to be used at public effort and expense by Sacramento County at some combination of Franklin Field and Sac Exec. Otherwise the Mustang capacity expansion is a good plan to serve General Aviation in the area of Elk Grove and Galt.

It would also be appropriate for the Bee to note the public value of General Aviation (GA) to be an answer to fear instead of a cause for it.

General Aviation serves public safety by routinely providing volunteer services such as patient medevac, organ transport, and search and rescue. A more dramatic example was the role of GA immediately after the Loma Prieta earthquake: GA moved about 100 tons of emergency aid supplies through Reid-Hillview Airport to reach the Watsonville Airport while road access was cut off to the epicenter area. In the south Sacramento area floods are a greater risk than earthquakes: Franklin Field is in the flood plain of the Sacramento River; Mustang is about 25 feet higher than Franklin Field.

General Aviation serves the public more routinely through service to private enterprise. It's not just corporate jets, single-engine Cessnas and the like do a good share of duty to carry consultants to clients and to bring small business owners to both customers and vendors. However, many private pilots would volunteer that the real value is in the personal pleasures of flying. Just as TV commercials say, that's priceless.

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