Editing Boeing 737 (section)

=== Airframe ===
The fuselage cross section and nose are derived from that of the [[Boeing 707]] and [[Boeing 727]]. Early 737 cockpits also inherited the "eyebrow windows" positioned above the main glareshield, which were a feature of the original 707 and 727<ref name="eyebrow">{{cite web |url=http://www.ppgaerospace.com/getmedia/ba64914b-c114-46bb-8cc4-c2ab09d440ee/B737_TD_FINAL.pdf.aspx?ext=.pdf |title=Cockpit Windows Next-Generation 737, Classic 737, 727, 707 Airplanes |publisher=PPG Aerospace Transparencies |access-date=August 27, 2015 |archive-date=September 4, 2015 |archive-url=https://web.archive.org/web/20150904131052/http://www.ppgaerospace.com/getmedia/ba64914b-c114-46bb-8cc4-c2ab09d440ee/B737_TD_FINAL.pdf.aspx?ext=.pdf |url-status=live}}</ref> to allow for better crew visibility.<ref>{{cite web |title=Boeing Next-Generation 737 Gets a Face-Lift |url=http://boeing.mediaroom.com/2005-01-26-Boeing-Next-Generation-737-Gets-a-Face-Lift |website=Boeing Media Room |publisher=Boeing |access-date=March 25, 2018 |archive-date=March 26, 2018 |archive-url=https://web.archive.org/web/20180326064213/http://boeing.mediaroom.com/2005-01-26-Boeing-Next-Generation-737-Gets-a-Face-Lift |url-status=live}}</ref> Contrary to popular belief, these windows were not intended for [[celestial navigation]]<ref>{{cite web |last1=Wallace |first1=James |title=Aerospace Notebook: New Boeing 717 design is bound to lift quite a few eyebrows |url=https://www.seattlepi.com/business/article/Aerospace-Notebook-New-Boeing-717-design-is-1085849.php |website=seattlepi.com |date=April 24, 2002 |publisher=Hearst Seattle Media, LLC |access-date=March 25, 2018 |archive-date=July 3, 2018 |archive-url=https://web.archive.org/web/20180703075821/https://www.seattlepi.com/business/article/Aerospace-Notebook-New-Boeing-717-design-is-1085849.php |url-status=live}}</ref> (only the military T-43A had a sextant port for star navigation, which the civilian models lacked.){{sfn|Sharpe|Shaw|2001|p=[https://archive.org/details/boeing737100200a00mich/page/37 37]|ps=}} With modern avionics, the windows became redundant, and many pilots placed newspapers or other objects in them to block out sun glare. They were eliminated from the 737 cockpit design in 2004, although they are still installed on customer request.{{sfn|Brady|2014|pages=144–145}} The eyebrow windows were sometimes removed and plugged, usually during maintenance overhauls, and can be distinguished by the metal plug which differs from the smooth metal in later aircraft that were not originally fitted with the windows.{{sfn|Brady|2014|pages=144–145}}

The 737 was designed to sit relatively low to the ground to accommodate the design of smaller airports in the late 1960s which often lacked [[Jet bridge|jetbridges]] or [[Ground support equipment#Belt loaders|motorized belt loaders]]. The low fuselage allowed passengers to easily board from a [[Ground support equipment#Passenger boarding steps/stairs|mobile stairway]] or [[airstair]]s (which are still available as an option on the 737 MAX) and for luggage to be hand-lifted into the cargo holds. However, the design has proved to be an issue as the 737 has been modernized with larger and more fuel efficient engines.<ref>{{Cite web |last=Vartabedian |first=Ralph |date=March 15, 2019 |title=How a 50-year-old design came back to haunt Boeing with its troubled 737 Max jet |url=https://www.latimes.com/local/california/la-fi-boeing-max-design-20190315-story.html |access-date=February 5, 2024 |website=[[Los Angeles Times]] |language=en-US}}</ref>

The 737's main landing gear, under the wings at mid-cabin, rotates into wheel wells in the aircraft's belly. The legs are covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells. The sides of the tires are exposed to the air in flight. "Hub caps" complete the aerodynamic profile of the wheels. It is forbidden to operate without the caps, because they are linked to the ground speed sensor that interfaces with the anti-skid brake system. The dark circles of the tires are clearly visible when a 737 takes off, or is at low altitude.<ref>Dekkers, Daniel, et al. (Project 2A2H). [home.deds.nl/~hink07/Report.pdf "Analysis Landing Gear 737-500."]{{dead link|date=November 2014}} ''Hogeschool van Amsterdam. Aviation Studies.'' October 2008. Retrieved: August 20, 2011.</ref>

From July 2008, the steel landing gear [[brake]]s on new NGs were replaced by [[Messier-Bugatti]] carbon brakes, achieving weight savings to {{Convert|550|–|700|lb}} depending on whether standard or high-capacity brakes were equipped.<ref name=cfb>Volkmann, Kelsey. [http://www.bizjournals.com/stlouis/stories/2008/08/04/daily27.html "Boeing gets OK for new carbon brakes."] {{Webarchive|url=https://web.archive.org/web/20081008094401/http://www.bizjournals.com/stlouis/stories/2008/08/04/daily27.html |date=October 8, 2008}} ''St. Louis Business Journal'' via ''bizjournals.com.'' Retrieved: April 22, 2010.</ref> On a 737-800 this gives a 0.5% improvement in fuel efficiency.<ref>Wilhelm, Steve. [http://www.bizjournals.com/seattle/stories/2008/08/11/story13.html "Mindful of rivals, Boeing keeps tinkering with its 737."] {{Webarchive|url=https://web.archive.org/web/20121026075536/http://www.bizjournals.com/seattle/stories/2008/08/11/story13.html |date=October 26, 2012}} ''Puget Sound Business Journal'', August 8, 2008. Retrieved: January 21, 2011.</ref>

737s are not equipped with [[fuel dump systems]]. The original design was too small to require this, and adding a fuel dump system to the later, larger variants would have incurred a large weight penalty. Boeing instead demonstrated an "equivalent level of safety". Depending on the nature of the emergency, 737s either circle to burn off fuel or land overweight. If the latter is the case, the aircraft must be inspected by maintenance personnel for damage before being returned to service.<ref>{{cite web|title=Boeing Commercial Aircraft – In-Flight Fuel Jettison Capability |url=http://www.boeing.com/assets/pdf/commercial/airports/faqs/fueldump.pdf |publisher=Boeing |access-date=November 23, 2014 |archive-date=March 10, 2015 |archive-url= https://web.archive.org/web/20150310192604/http://www.boeing.com/assets/pdf/commercial/airports/faqs/fueldump.pdf|url-status=live}}</ref><ref>Cheung, Humphrey. [http://www.tgdaily.com/trendwatch-features/39149-troubled-american-airlines-jet-lands-safely-at-lax "Troubled American Airlines jet lands safely at LAX."] {{Webarchive|url=https://web.archive.org/web/20120606152043/http://www.tgdaily.com/trendwatch-features/39149-troubled-american-airlines-jet-lands-safely-at-lax |date=June 6, 2012}} ''tgdaily.com,'' September 2, 2008. Retrieved: August 20, 2011.</ref>

<gallery mode="packed" heights="140">
File:Boeing 737-200 planform view.jpg|Original 737 with [[JT8D]] engines that span the entire [[Chord (aeronautics)|wing chord]]
File:Transaero b737-400 planform ei-cxk arp.jpg|[[737 Classic]] with larger [[CFM56]] engines mounted mostly ahead of the wing
File:American Boeing 737-800 N886NN planform.jpg|alt=The 737NG with improved CFM56-7 engines and redesigned larger wing|[[737 Next Generation]] with improved CFM56-7 engines and redesigned wing
File:United Boeing 737-8 MAX N17322 planform.jpg|[[737 MAX]] with larger [[CFM LEAP]] engines, mounted even further ahead of the wing
</gallery>