phumbe

The other two replies covered your questions well, so I'll just add that wakes don't descend particularly fast. According to the FAA's Pilot's Handbook of Aeronautical Knowledge[1] (page 14-28), "Tests have also shown that the vortices sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft."

Considering the Challenger's encounter with the A380's wake, it took 1-2 minutes for the Challenger to hit the wake, so the wake probably had 1-3 minutes to make the 1000-foot descent. That very roughly fits the expected "several hundred feet per minute" descent rate.

Considering the case of refueling, the wake's motion downward is much slower than the aircrafts' horizontal motion, so it wouldn't have descended much by the time it's left behind entirely.

[1] Available for free at https://www.faa.gov/regulations_policies/handbooks_manuals/a...

Glad you brought up winglets. My favorite example are those on the new 737 MAX. Boeing's page[1] about them is top-notch.

[1] http://www.boeing.com/commercial/737max/737-max-winglets/

It's helpful to think of an aircraft's wake in two parts.

The wing is deflecting air downward to provide lift; this creates a volume of downward-moving air behind the aircraft.

There's higher pressure under the wing and lower pressure on top, so air from below tries to get above the wing at the wingtips. This causes circulatory motion, yielding wingtip vortices (see my top-level comment for some visualizations).

To add to jacquesm's response, the footage in [2] is definitely from a humid day. That makes condensation happen very readily.

If I remember correctly, the trails from the outboard edges of the flaps are just like wingtip vortices. The airfoil's geometry suddenly changes, acting like a wingtip and creating a vortex.

That's Gol Transportes Aéreos Flight 1907 -- https://en.wikipedia.org/wiki/Gol_Transportes_A%C3%A9reos_Fl...

There's also an episode ("Phantom Strike") of the TV series Mayday about the incident; it's probably on youtube.

For anyone interested, there are several great youtube videos[1-4] that show the wakes (the wingtip vortices in particular) created by various aircraft.

This incident brings the Reduced Vertical Separation Minima (RVSM)[5] into question. Strategic Lateral Offset Procedure (SLOP)[6] can be used used to avoid such incidents.

[1] https://www.youtube.com/watch?v=E1ESmvyAmOs

[2] https://www.youtube.com/watch?v=dfY5ZQDzC5s

[3] https://www.youtube.com/watch?v=uy0hgG2pkUs

[4] https://www.youtube.com/watch?v=KXlv16ETueU

[5] https://en.wikipedia.org/wiki/Reduced_vertical_separation_mi...

[6] https://en.wikipedia.org/wiki/Strategic_lateral_offset_proce...

Superb! But I might have to look at the code for calculating the Board's mood. $3.2M in cash and a profit goal of $1.3M makes me unfortunately wary of spending on large research/special projects or hiring additional staff.

Looks like forward slip to landing has been in the Private Pilot Practical Test Standards [1] since at least Nov 2011

[1][PDF] https://www.faa.gov/training_testing/testing/test_standards/...

The APU provides electrical power but only when there's fuel for it to burn. In the case of the Gimli Glider, it therefore would not have worked.

If we look at the case of Cactus 1549 [1], though, we see Capt. Sullenberger turned on the APU immediately after both engines failed. This has been hailed [1,2] as a good decision -- no doubt because the A320 relies so heavily on electronics for control and it could have helped them restart the failed engines.

Commercial jets certainly do also carry traditional batteries for various uses. Take the Boeing 787 as an example; its onboard batteries originally presented a fire hazard [3].

[1] https://en.wikipedia.org/wiki/US_Airways_Flight_15494

[2][PDF] http://www.ntsb.gov/investigations/AccidentReports/Reports/A...

[3] https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_...