Editing Boeing 707 (section)

===Wings===
The 707's wings are swept back at 35°, and like all swept-wing aircraft, display an undesirable "[[Dutch roll]]" flying characteristic that manifests itself as an alternating combined yawing and rolling motion. Boeing already had considerable experience with this on the B-47 and B-52, and had developed the [[yaw damper]] system on the B-47 that would be applied to later swept-wing configurations like the 707. However, many pilots new to the 707 had no experience with this instability as they were mostly accustomed to flying straight-wing propeller-driven aircraft such as the [[Douglas DC-7]] and [[Lockheed Constellation]].

On one customer-acceptance flight, where the yaw damper was turned off to familiarize the new pilots with flying techniques, a trainee pilot's actions violently exacerbated the Dutch roll motion and caused three of the four engines to be torn from the wings. The plane, a brand new 707-227, ''N7071'', destined for Braniff, [[1959 Washington Boeing 707 crash|crash-landed]] on a river bed north of Seattle at [[Arlington, Washington]], killing four of the eight occupants.<ref>{{ASN accident|id=19591019-0}}</ref>

In his autobiography, [[test pilot]] Tex Johnston describes a Dutch roll incident he experienced as a passenger on an early commercial 707 flight. As the aircraft's movements did not cease and most of the passengers became ill, he suspected a misrigging of the directional autopilot (yaw damper). He went to the cockpit and found the crew unable to understand and resolve the situation. He introduced himself and relieved the ashen-faced captain who immediately left the cockpit feeling ill. Johnston disconnected the faulty autopilot and manually stabilized the plane "with two slight control movements".<ref>{{cite book |last=Johnston |first=A.M. |title=Tex Johnston: Jet-Age Test Pilot |publisher=[[Smithsonian Books]] |date=December 2000 |page=247 |isbn=978-1-56098-931-8 |url=https://books.google.com/books?id=wcJvDwAAQBAJ&pg=PT248}}</ref>

Johnston recommended Boeing increase the height of the [[Vertical stabilizer|tail fin]], add a boosted rudder as well as add a [[Empennage#Fins|ventral fin]]. These modifications were aimed at mitigating Dutch roll by providing more directional stability in [[Aircraft principal axes|yaw]].<ref>{{cite book |last1=Johnston |first1=A.M. "Tex" |title=Tex Johnston, Jet-Age Test Pilot |date=1992 |publisher=Bantam |isbn=9780553295870 |location=New York |pages=267–268}}</ref>