saintsman
Posts: 2037
Joined: Fri Mar 15, 2002 12:34 am

Ground / Flight Switch

Mon Sep 08, 2003 8:14 pm

The 'window heat' thread made me think of this. Is it a common term on all large aircraft or do some have a different name?

For those unaware what it is, some aircraft systems are only required when the aircraft is flying (like the window heat) and these are controlled by micro switches attached to the undercarriage (weight-on microswitches that operate when the undercarriage is extended or compressed - in the air or on the ground). You may need to test a system on the ground so you need to over ride the weight-on and this is done by operating the Ground / Flight switch. It is one of those things I have never thought about before - is it called that by every one?
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Ground / Flight Switch

Mon Sep 08, 2003 8:39 pm

Most common in-use that I'm aware of are "squat switch" and "air-ground switch" (or sensor)....
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
avioniker
Posts: 1099
Joined: Tue Jan 01, 2002 5:38 am

RE: Ground / Flight Switch

Mon Sep 08, 2003 9:57 pm

Don't forget the WOW system that incorporates wheel spin-up and gear compression to determine Weight On Wheels for many systems.
Going back to the original thread, how many aircraft use air-ground sensing for the windshield heat? I can't think of any offhand. Then again I might be having a "pre-senior" moment again.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
saintsman
Posts: 2037
Joined: Fri Mar 15, 2002 12:34 am

RE: Ground / Flight Switch

Mon Sep 08, 2003 10:24 pm

Avioniker,

How is inadvertant windscreen over heat avoided on the ground. Just thermostats? My large aircraft experience is limited to just one type (VC-10)

regards,

Saintsman
 
FDXmech
Posts: 3219
Joined: Sun Mar 19, 2000 9:48 pm

RE: Ground / Flight Switch

Mon Sep 08, 2003 11:33 pm

On many aircraft, pulling the ground sensing circuit breaker/s will put the aircraft in flight mode.

This because most systems utilize relays to determine flight or ground mode. These relays are energized on the ground and deenergized in flight (fail-safe, you wouldn't want a flt/gnd relay to fail inflight causing the aircraft or system to revert to ground mode).

You're only as good as your last departure.
 
avioniker
Posts: 1099
Joined: Tue Jan 01, 2002 5:38 am

RE: Ground / Flight Switch

Tue Sep 09, 2003 1:22 am

All currently certified windshield heat systems have a thermostat control. Some use thermistor some have an actual heat actuated switch but, yes, the windshield heat is thermostat controlled, on the ground as well as in flight.
Problem is they break and windshields do overheat so leaving them on on the ground is never a good idea unless you're in a really cold environment where you want to prevent thermal shock.
Fairbanks comes to mind...
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
citationjet
Posts: 2258
Joined: Sun Mar 09, 2003 2:26 am

RE: Ground / Flight Switch

Tue Sep 09, 2003 2:07 am

If you use popsicle sticks to disable the Weight On Wheels (WOW) switch, be sure to remove them.

Mechanics Blamed for GV Hard Landing
According to the NTSB, General Dynamics Aviation Services maintenance personnel in Palm Beach, Fla., failed to remove popsicle sticks that were being used to disable the weight-on-wheels (WOW) switches of a Gulfstream V on jacks. That led to a hard landing causing substantial damage to the airplane, according to the NTSB’s final report of the Feb. 14, 2002 incident. Shortly after departure, the pilot requested a return for landing because the landing gear would not retract. As the jet flared for landing and the crew pulled back the power levers to idle, the spoilers deployed because of the disabled WOW switches. Flight data recorder information showed that the spoilers deployed when the airplane was nearly 60 feet high. The airplane hit the runway at a vertical acceleration of 4.25 g, driving the right main gear through the wing and rupturing a fuel tank. The aircraft, N777TY, was registered to BB Five, Wilmington, Del., and operated for Ty Inc., Oakland, Ill.

Cost of popsicle sticks: 40 cents
Cost of a G-V: $40M
Look on the pilots' face after landing: Priceless



[Edited 2003-09-08 19:17:55]
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Ground / Flight Switch

Tue Sep 09, 2003 2:49 am

Window Heat controls window temperature to approx 95-105 degrees (depending on the Boeing type). When window temp is in that temp range, the window heat control unit either cuts power to the window or the pwr output to the window is minimal.

On the B777, window heat is always left on. If you turn it off, it actual reverts to backup window heat mode which is actually hotter than normal mode.
 
Minuteman
Posts: 260
Joined: Sat Aug 05, 2000 1:01 am

RE: Ground / Flight Switch

Tue Sep 09, 2003 10:06 am

Its not all microswitches. The 777 also has strain gauges on the gear.
 
MxCtrlr
Posts: 2312
Joined: Tue Nov 13, 2001 11:22 am

RE: Ground / Flight Switch

Tue Sep 09, 2003 11:54 am

The window heat and Flight/Ground Shift have nothing in common with each other. Pitot/Static Heaters however DO shift to high heat mode when the aircraft is in flight configuration.

MxCtrlr  Smile/happy/getting dizzy
Freight Dogs Anonymous - O.O.T.S.K.  Smokin cool
DAMN! This SUCKS! I just had to go to the next higher age bracket in my profile! :-(
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Ground / Flight Switch

Wed Sep 10, 2003 5:51 am

MxCtrlr
Which aircraft have that feature? The only Boeing jet that I know of that has that feature is the B777.

Who is online

Users browsing this forum: No registered users and 13 guests