Perhaps you’ve observed the small windows perched above the main cockpit windows in vintage aircraft like the classic Boeing 737s, DC-8s, DC-9s, and 707s. Interestingly, these petite windows seem absent from contemporary planes like the 787, the latest 737 MAX, Airbus A320, 777, among others. So, what exactly were these small windows? Known as eyebrow windows, these features were present in a number of aircraft, including the Boeing 737, McDonnell Douglas MD-80, and other historical planes. They weren’t merely decorative but served a specific purpose, which I’ll talk about further here.
Visibility During Turns
The eyebrow windows have long graced the cockpits of various aircraft including the famed Boeing 737 and DC-8. At the core of their design was the aim to enhance visibility, particularly during turns. They were more beneficial for pilots on the left side when veering right and vice versa. Interestingly, despite their crucial role in improving pilots’ field of vision, these eyebrow windows did not find their place in later Boeing designs. In fact, the modern versions of the 737 have completely done away with them, though the recesses marking their previous positions are still visible.
Celestial Navigation and the Role of Eyebrow Windows
Before the era of Inertial Navigation Systems (INS) and Inertial Reference Systems (IRS), pilots had to rely heavily on celestial navigation for night flying. In these instances, the aircraft had little to no reference to the ground. Celestial navigation is a method that relies on heavenly bodies to determine the aircraft’s position. It was the on-board navigator’s responsibility to execute this method, typically with the help of a sextant.
Eyebrow windows played a crucial role in this context. They provided a broad view of the sky, aiding the star-based navigation system. The DC-8, for example, had a specific viewing hole in the cockpit ceiling designed for this purpose. It was a critical component in an era when aircraft often required an additional navigator crew member for such navigation methods.
The Decline of Eyebrow Windows
As technology advanced, the relevance and usefulness of eyebrow windows began to fade. Today’s navigation systems heavily rely on computers and satellite assistance, rendering visual aids like eyebrow windows less necessary. Clear vision is still crucial, but with the development of advanced systems such as improved instrument landing systems and Traffic Collision Avoidance System (TCAS), the need for eyebrow windows decreased significantly.
Despite their decreasing usefulness, eyebrow windows remained a feature on many Boeing planes, including several variants of the 737. However, the Boeing 757 marked a break from this trend, with its redesigned cockpit that did not include eyebrow windows. Some other aircraft, like the McDonnell Douglas MD-80, continued the use of eyebrow windows, although their use in the industry is progressively decreasing.
Rationale behind the Discontinuation of Eyebrow Windows
The discontinuation of eyebrow windows was not just a matter of technological advancement. Other factors contributed to this decision, too. Aircraft design typically aims to be efficient and cost-effective. Keeping the eyebrow windows in place would mean additional maintenance, translating into increased costs and time. Furthermore, removing these windows has a minor positive effect on the aerodynamics of the plane, contributing to better fuel economy.
Pilots also reported that the added glare from these windows was more of a hindrance than a help. Additionally, getting rid of these windows helped reduce noise in the cockpit, a common complaint with earlier 737 aircraft.
Indeed, Boeing shed light on their rationale behind this design evolution in a 2005 press release regarding the 737 production. The company stated that the design modification leads to a reduction in airplane weight by 20 pounds and saves around 300 hours of routine inspections per airplane.
This accounts for why we no longer see eyebrow windows on modern aircraft. They had their moment in the limelight on the 737, MD-80, 707, and a host of other aircraft, but technological advancements have rendered them unnecessary. However, it’s noteworthy that such technological evolution has undoubtedly made aviation safer and more efficient. So, hopefully, this clarifies what those small windows atop the main cockpit windows were in those classic planes!
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
