By Allison Lynch, Ewa Niechwiej-Swedo PhD, Shi Cao PhD, Suzanne Kearns PhD, and Elizabeth Irving OD, PhD.

University of Waterloo 
Waterloo Institute for Sustainable Aeronautics (WISA)
Waterloo, Ontario, Canada

The aviation industry has an excellent record of flight safety – due, in part, to stringent pilot medical standards. However, it is possible that some of these standards could be outdated or unnecessarily strict. 

Would safety be compromised if some medical standards were cautiously adjusted, based on evidence collected from pilots in operations? 

Many pilots left the industry during the pandemic, and as pilots have a shorter career length than many other professions due to mandatory retirement ages, research to improve the retention of existing pilots is essential. 

Distance vision standards require corrected or uncorrected vision of 20/20 in each eye separately for both Class 1 and Class 2 medicals (required for airline transport pilots and commercial pilots, respectively). The vision standards required for private pilots is 20/40 vision corrected or uncorrected in each eye separately. 

The numbers represent your vision compared to someone with “normal” vision. The top number is the distance you need to be to see something, whereas the bottom number is the distance that a person with “normal” vision could be to see the same thing. For example, 20/40 means that the person being tested needs to be 20ft away from an object that an individual with “normal” vision could see at 40ft away (therefore your vision is worse than normal). 

However, these standards are not solidly rooted in evidence and could be considered unintentionally discriminatory. These stringent visual standards may be restricting the pool of eligible pilots and adversely impacting the retention of experienced pilots. 

Our researchers at the University of Waterloo are examining current vision acuity requirements for pilots to determine how evidence-based adjustments in these standards might impact professional competency and flight safety.

To explore how worsened vision impacts pilot performance, our research is conducted in an Alsim AL250 flight simulator configured as a Cessna 172. Our first experiment involved novice pilots with 0 to 300 flight hours. We started by simulating a calm, clear day and asked pilots to fly a downwind-to-final approach and land. Each pilot’s vision was degraded with glasses jokingly called “beer goggles” by participants because they mimic visual blurriness that is often associated with excessive drinking. The simulator and “goggles” allow researchers to safely monitor pilot performance at 6 decreasing levels of vision ranging from normal 20/20 to no vision at all. 

Left to right: 20/20, 20/30, 20/40, 20/100, 20/200, No Vision. Image credit: University of Waterloo

Pilots also rated how much stress they were experiencing – and task difficulty – as vision was decreased. Not surprisingly, all pilots failed to land the aircraft safely with zero vision. 

Interestingly though, pilots were very successful at landing with vision considerably worse than existing medical standards. Novice pilots, with visual impairment of 20/200 (equivalent to the Big E of an eye chart) were able to safely land the aircraft on the runway without any effect on flight performance. Despite the successful landing, the novice pilots reported increased stress and difficulty when their vision was degraded to just 20/40 (vision required to read a newspaper). 

 Some participant responses during the high-stress trials included: 

• “Began losing sense of some instruments and situational awareness”,
• “Couldn’t tell the PAPI light colors even when I was about 1nm from the threshold”, and
• “While getting close to the runway, as I slow down the plane, I had an illusion of stalling or not going forward, and it was stressful”. 

This suggests that even though the task was completed successfully, there may be workload demands that are elevated with even small visual impairments which could impact performance during more difficult tasks. 

Simulated vision loss is not the same as long-standing vision loss. Typically, for people who lose their vision, they slowly adapt and make adjustments to their lifestyle to manage the change in vision. 

It would be interesting to study experienced pilots who have had their licences revoked because they no longer meet current visual medical standards. It may be that these experienced pilots not only can pilot the aircraft successfully but also may experience less stress and difficulty as they have adapted their piloting to their decreased vision. It is currently unknown how many pilots have lost their licence due to reduced vision. 

We know that factors such as decreased illumination and weather conditions reduce visibility even when vision is normal. Our follow-up experiments explore the performance impact of more challenging flight conditions (e.g. wind, rain) with degraded vision. Initial findings suggest that vision can still be significantly degraded (below current medical standards) before performance is impacted. 

Overall, our evidence indicates that pilots in training are capable of flying and landing an aircraft with various levels of vision degradation that are worse than the existing medical standards. 

The point of this research is not to suggest that pilots be allowed to fly with impaired vision of 20/400 or 20/800, but that current visual standards of corrected 20/20 may be unnecessarily stringent and result in career aviators losing their medical certificates or potential new aviators not being able to obtain one. A re-evaluation of the current visual standards for pilots could result in those with less than 20/20 vision to enter the profession and allow experienced pilots to remain in their careers for a longer period. 

Updated evidence-based medical standards would support a sustainable and equitable workforce within our industry in a way that is often overlooked. Any proposed reduction in vision requirements will require careful consideration and examination.