Overview
Method Seven designs and produces technical eyewear to color correct, balance light and optimize vision in intense lighting situations. We create exceptional aviation eyewear using pristine, clear crystal glass lenses, modified to eliminate harmful ultraviolet energy, attenuate uncomfortable infrared heat, and reduce specific portions of the visible light spectrum to provide contrast. Our lenses enhance a pilot’s ability to see well over distance, to maintain natural peripheral vision, to more easily focus, and to recognize contrast when looking towards clouds or instrument panels.
We design lenses to address problems that pilots have shared with us. Pilots also shared concerns about sun exposure in their cockpits. Recognizing they are getting sunburned, developing skin cancers, and suffering degeneration in their vision, they want to know more about how well their windscreens protect them from exposure to UVA light.
There is an excellent study on this subject sponsored by the Federal Aviation Administration (FAA), and conducted by the Civil Aerospace Medical Institute (CAMI). Their report, published in July 2007, is entitled, Optical Radiation Transmittance of Aircraft Windscreens and Pilot Vision. In this study, CAMI evaluated how well the windscreens from 3 commercial jets, 2 commercial propeller driven passenger planes, 1 small private jet, and 2 small general aviation single-engine propeller-driven planes, filtered out UVA light. Aside from the data of eight aircraft windscreens evaluated in this study, there is scant information available as to how other windscreens perform.
Method Seven Laboratories, the technical arm of Method Seven, set out to assess as many windscreens as possible. With a device called a spectrometer, M7 labs evaluates how lenses filter light across the ultraviolet, visible, and beginning near infrared portion of the light spectrum. The same technology is applicable to evaluate the extent that windscreens filter out ultraviolet light in the UVA region. To date, M7 Labs has characterized the windscreens on 73 different aircraft. These results, minus the identification of some models of aircraft, are shared and discussed in this report.
Method Seven Labs believes the safety committees of pilot unions and associations would be interested in reviewing all data. We also believe that this study represents a start to a broader discussion and further investigation of how well windscreens and other cockpit windows protect pilots from UVA radiation. We would like to discuss our results with the appropriate leadership within pilot associations. Contact information is listed at the end of this report.
Pilots and Ultraviolet radiation
There are three regions of ultraviolet light - UVC, UVB, or UVA. UVC, with the shortest wavelength (100 – 280 nm), carries the most energy, and is the deadliest of these regions. Fortunately, UVC is completely absorbed by the earth’s ozone layer, and except for certain regions over the poles, seldom reaches the altitude where aircraft fly. UVB (280 – 315 nm), is also damaging to human tissue but is largely blocked out by our atmosphere; it is filtered out by almost all glass and plastic windows and screens. UVA (315 – 380 nm), is lower energy and less destructive, but can penetrate more deeply into human tissue. UVA cumulatively damages and can impair the iris and lens in our eyes, and damage a pilot’s skin over time.
As pointed out in the ‘Optical Radiation’ report published in July 2007, some windscreens do an excellent job of filtering out UVA light - but not all. UVA is a pronounced problem for pilots because the intensity of UVA radiation increases approximately 15% for every 3,000 feet of altitude above sea level. This means a commercial pilot flying at 33,000 feet is flying in a UVA environment that is 4.7 times as intense as experienced at sea level. It is logical that pilots who fly for long hours during daylight wish to know how well their windscreens are filtering out UVA.
M7 Labs Methodology
In the 2007 FAA study, airplane manufacturer’s sent eight windscreens to the CAMI Vision Research Laboratory in Oklahoma City, OK. Testing was performed under ideal laboratory conditions using calibrated light sources. In the M7 Labs study, the ambient light spectrum is recorded using a spectrometer in-situ.
In Figure 1, you see the intensity of light as it varies across different wavelengths, and as captured by a spectrometer. The various regions; ultraviolet-A (UVA), visible (VIS), and near infrared (NIR), are identified. The shape of this spectrum will change depending on whether the sun is overhead or on the horizon, and whether the day is clear or cloudy.
In the M7 Labs study, we first measure the spectrum of light shining towards the aircraft windscreen and then we measure the spectrum of light passing through the windscreen. From these two data sets, we calculate the ratio of total UVA energy passing through the windscreen divided by the total UVA energy of the sunlight shining towards the windscreen. This provides a calculated value for the percentage of UVA that passes through the windscreen.
This method is less precise than the results obtained by CAMI because there can be a change in the intensity of sunlight between the two measurements. Results, however, are sufficiently accurate to clearly demonstrate whether a problem exists, and to identify the approximate magnitude of that problem. Further, this in-situ test technique allowed M7 Labs to measure a larger number of samples than CAMI.
Exemplified in Figure 2, you see the intensity of light directed at the windscreen and the intensity of light that passes through the windscreen. It is evident that some light in the UVA range is present in the cockpit. With mathematical integration, we are able to calculate the total energy of each curve and then calculate that approximately 20% of UVA light passed through this particular windscreen. Figure 3 exemplifies a windscreen that does not allow any UVA light into the cockpit.
The Effect of Altitude on UVA Exposure
Method Seven Labs researched the service ceiling for each aircraft in the study, because altitude plays a key role in how much UVA a pilot may be exposed to. For example, the service ceiling for the Embraer EMB-505 aircraft is 45,000 feet. The amount of UVA light present at this altitude is 8 times greater than the amount of UVA light present at sea level.
The Embraer EMB-505 aircraft allows 14% of UVA light to pass through the windscreen. The effective UVA exposure in an Embraer cockpit, at 45,000 feet, would be 14% times 8.1, or 110% of the exposure a person would experience at sea level.
Results
Table 1 shows an overall tabulation of UVA measurement results identified by major categories. Of the 73 aircraft tested, 45 windscreens removed 100% of the UVA light. 7 aircraft, however, allowed 30% or more UVA light to enter through the windscreen.
There is a wide range of service ceilings for the various aircraft that were tested. The highest service ceiling was 51,000 feet and the lowest was 5,000 feet. These statistics are provided in Table 2. With such a wide range in likely flight altitudes, it was important to factor into the study the effect of the various service ceilings.
Key data from the study is provided in Table A. In the last column of Table A we provide the calculated amount of UVA a pilot would be exposed to in each cockpit flying near the service ceiling, as referenced to UVA exposure at sea level. For example, a value of 1.5X indicates a pilot would be exposed to 50% more UVA light coming through the windscreen of that particular plane as they would sitting unprotected on the beach.
Table A. Windscreen Transmittance of UVA vs. Unprotected UVA Exposure At Sea Level
| Make |
Model |
% UVA |
Service Ceiling (ft) |
Sea Level Factor |
Equivalent Sea Level Exposure |
| Cessna |
Citation X |
20% |
51,000 |
10.8 |
2.2 x |
|
|
42% |
35,000 |
5.1 |
2.1 x |
|
|
45% |
33,000 |
4.7 |
2.1 x |
|
|
20% |
50,000 |
10.3 |
2.1 x |
|
|
64% |
18,000 |
2.3 |
1.5 x |
|
|
35% |
30,000 |
4.0 |
1.4 x |
|
|
48% |
18,950 |
2.4 |
1.2 x |
|
|
36% |
25,000 |
3.2 |
1.1 x |
|
|
14% |
45,000 |
8.1 |
1.1 x |
|
|
15% |
43,100 |
7.4 |
1.1 x |
|
|
18% |
35,000 |
5.1 |
0.9 x |
|
|
16% |
35,000 |
5.1 |
0.8 x |
|
|
14% |
35,000 |
5.1 |
0.7 x |
|
|
45% |
5,000 |
1.3 |
0.6 x |
|
|
15% |
27,000 |
3.5 |
0.5 x |
|
|
13% |
15,000 |
2.0 |
0.3 x |
|
|
9% |
20,700 |
2.6 |
0.2 x |
|
|
8% |
18,000 |
2.3 |
0.2 x |
|
|
6% |
20,000 |
2.5 |
0.2 x |
|
|
8% |
13,000 |
1.8 |
0.1 x |
|
|
5% |
20,000 |
2.5 |
0.1 x |
|
|
5% |
20,000 |
2.5 |
0.1 x |
|
|
6% |
15,100 |
2.0 |
0.1 x |
|
|
4% |
20,000 |
2.5 |
0.1 x |
|
|
3% |
21,000 |
2.7 |
0.1 x |
|
|
4% |
13,000 |
1.8 |
0.1 x |
|
|
2% |
20,000 |
2.5 |
0.1 x |
|
|
3% |
12,000 |
1.7 |
0.1 x |
| Autogyro |
Cavalon |
0% |
10,000 |
1.6 |
0 x |
| Icon |
Icon A5 |
0% |
15,000 |
2.0 |
0 x |
| Skyreach |
Bush Cat |
0% |
12,000 |
1.7 |
0 x |
| Pipistrel |
Taurus |
0% |
12,100 |
1.8 |
0 x |
| Stemme |
S-12 |
0% |
12,500 |
1.8 |
0 x |
| Cessna |
172N |
0% |
13,000 |
1.8 |
0 x |
| Diamond Aircraft |
DA20-C1 |
0% |
13,100 |
1.8 |
0 x |
| CubCrafters |
Carbon Cub |
0% |
14,000 |
1.9 |
0 x |
| Lockwood Aircraft |
Aircam |
0% |
15,000 |
2.0 |
0 x |
| American Champion |
8KCAB |
0% |
15,800 |
2.1 |
0 x |
| Piper |
PA-22-150 |
0% |
16,500 |
2.2 |
0 x |
| Beechcraft |
B35 |
0% |
17,100 |
2.2 |
0 x |
| Piper |
Seminole P44-180 |
0% |
17,100 |
2.2 |
0 x |
| Cirrus |
SR-22T |
0% |
17,500 |
2.3 |
0 x |
| Cirrus |
Carbon |
0% |
17,500 |
2.3 |
0 x |
| Cirrus |
Platinum |
0% |
17,500 |
2.3 |
0 x |
| Diamond Aircraft |
DA42-VI |
0% |
18,000 |
2.3 |
0 x |
| Slim Aviation |
Savage |
0% |
18,000 |
2.3 |
0 x |
| TL Ultralight |
Sting S4 |
0% |
18,000 |
2.3 |
0 x |
| Cessna |
182S |
0% |
18,100 |
2.3 |
0 x |
| TL Ultralight |
TI3000 |
0% |
19,000 |
2.4 |
0 x |
| Beechcraft |
Baron G58 |
0% |
19,700 |
2.5 |
0 x |
| Aviat |
A-1C-180 |
0% |
20,000 |
2.5 |
0 x |
| Diamond Aircraft |
DA62 |
0% |
20,000 |
2.5 |
0 x |
| Velocity |
XM RG |
0% |
20,000 |
2.5 |
0 x |
| Pipistrel |
Virus SW |
0% |
20,300 |
2.6 |
0 x |
| Vans |
RV-7 |
0% |
22,500 |
2.9 |
0 x |
| Vans |
RV-10 |
0% |
22,500 |
2.9 |
0 x |
| Vans |
RV-7A |
0% |
22,500 |
2.9 |
0 x |
| Vans |
RV-10 |
0% |
22,500 |
2.9 |
0 x |
| Douglas |
DC-3 |
0% |
23,200 |
2.9 |
0 x |
| Mooney |
Acclaim Ultra - M20V |
0% |
25,000 |
3.2 |
0 x |
| Mooney |
Acclaim Type S |
0% |
25,000 |
3.2 |
0 x |
| Pilatus |
PC-6 |
0% |
25,000 |
3.2 |
0 x |
| Quest |
Kodiak 100 |
0% |
25,000 |
3.2 |
0 x |
| Vans |
RV-6A |
0% |
25,700 |
3.3 |
0 x |
| Lancair |
Evolution |
0% |
28,000 |
3.7 |
0 x |
| Stemme |
S-10 |
0% |
30,000 |
4.0 |
0 x |
| Daher |
TBM 700 |
0% |
31,000 |
4.2 |
0 x |
| Lockheed Martin |
C-5M Super Galaxy |
0% |
35,700 |
5.3 |
0 x |
| Cessna |
208B |
0% |
25,000 |
3.2 |
0 x |
| Airbus |
A321 |
0% |
41,000 |
6.8 |
0 x |
| Cessna |
Citation M2 |
0% |
41,000 |
6.8 |
0 x |
| Boeing |
747-8F |
0% |
43,100 |
7.4 |
0 x |
Concluding Comments
Most cockpit windscreens do a good to reasonable job of filtering out UVA light. However, because of the significant increase in UVA radiation at higher altitudes, even 25% of UVA light that passes through a windscreen can represent a worrisome amount of UVA for a pilot flying at 30,000 feet. Such a pilot would experience the same amount of UVA as they would experience while sunning at the beach.
Pilots need awareness of the amount of UVA that passes through the windscreens of their planes. Where UVA is present, pilots should wear protective glasses and clothing, and put on sunscreen.
Contact Information
Method Seven is available to discuss the full results of our study with pilots in any forum, association or union where may be appropriate. You may contact Method Seven to discuss by reaching out to info@methodseven.com
