juanchie
Posts: 188
Joined: Thu Jan 29, 2004 7:17 am

Backcourse/ ADF Questions

Sun Feb 27, 2005 11:15 am

I have been studyign the manual to a new sim addon of the 767 and would like to know what the backcourse option is on modern airplanes? I know approach, ils loc, heading lock and others but not backcourse.

On a seperate note, what is an adf and where do i find information on the frequency? I know VOR but not ADF. Any info from you guys would be great.


juanchie
God, forgive me for who I am, and help me be the man I want to be.
 
KYIPpilot
Posts: 1357
Joined: Fri Oct 24, 2003 11:14 pm

RE: Backcourse/ ADF Questions

Sun Feb 27, 2005 11:25 am

The backcourse is like flying an ILS, but backwards. For example, if a RWY 36 had an ILS, there could be a backcourse for RWY 18. It uses the back side of the ILS localizer and glideslope. If you are using a standard OBS VOR tracker, it "reverse senses," meaning when the needle is off to the left, you are actually to the LEFT of course, meaning you turn away from the needle. Normally you turn towards it to track it.

If you have a HSI, it automatically takes out the reverse sensing, and you fly like normal.

An ADF is an Automatic Direction Finder. It used NDB's, non-directional beacons on the ground, that send out a signal in all directions. The ADF in the airplane has a needle that always points in the direction of the station, no matter where you are in relation to it. You can use the needle to fly non-precision approaches. It It is the oldest radio nav system in use, and is slowly being phased out. They are not as accurate as VOR's, GPS, etc. NDB's are affected by lightning, and interference from other stations, among other things.

Sorry if this is not clear enough, I'm sure other can help!  Smile

[Edited 2005-02-27 03:29:34]
"It starts when you're always afraid; You step out of line, the man come and take you away" -Buffalo Springfield
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Backcourse/ ADF Questions

Sun Feb 27, 2005 11:36 am

It uses the back side of the ILS localizer and glideslope.

Just localizer (left-right). No glideslope information on a back-course.
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Backcourse/ ADF Questions

Sun Feb 27, 2005 11:42 am

Here's a link to backcourse information.


Here's a link to ADF/NDB information.


Here's a link to a useful VOR visualization tool.




Enjoy!


2H4


Intentionally Left Blank
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Backcourse/ ADF Questions

Sun Feb 27, 2005 12:30 pm

Interestingly enough, the only airline that I am aware of that insisted that all of their aircraft, had an autopilot/flight director mode that would automatically track the ILS backcourse...was PanAmerican.

This was required because they operated to many worldwide airports that had backcourse approaches...many years ago.

Many other inovations can be traced to PanAm as well...and their training was second to none.
 
KYIPpilot
Posts: 1357
Joined: Fri Oct 24, 2003 11:14 pm

RE: Backcourse/ ADF Questions

Sun Feb 27, 2005 12:44 pm

Ahh, I remember now, thats right. I have only done one backcourse ever. Thanks!
"It starts when you're always afraid; You step out of line, the man come and take you away" -Buffalo Springfield
 
OzLAME
Posts: 336
Joined: Thu Feb 17, 2005 8:40 am

RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 9:11 am

An HSI does not automatically take out the reverse sensing when flying a backcourse, as the Localiser signal only allows the Nav receiver to work out which side of the beam the aircraft is on. Aircraft with mechanical HSIs may have a Back Course switch, this is a multipole rotary switch that reverses the sense of the D-bar so that you can still 'fly to the needle' when on a backcourse. The Mitsubishi MU-2s I used to work on had them fitted on the outer LH instrument panel, just a little knob (IIRC) with an arrow on it labelled Front Course-Back Course. IIRC the switch also disables the g/s pointer.

Aircraft that I work on that have EHSIs fitted, automatically reverse the sense of the D-bar if the course needle is pointing more than 90 degrees off the a/c heading and the Nav receiver is selected to a Localiser frequency.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.
 
PhilSquares
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RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 5:31 pm

Maybe I'm missing something, but on a glass cockpit, you can build the approach in the FMS and fly it in LNAV. You could always use V/S to fly the descent profile.
Fly fast, live slow
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 5:36 pm

Not only that, Phil, but a few here have clearly never used an electro-mechanical HSI.
With most, set the inbound front course, and fly to the diviation bar...correct sensing will be provided, inbound on the back course, as well.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 6:08 pm

411A, you're right. I do remember those days! Seems like a million years ago, now I'm having flashbacks of the old J8 attitude indicator and doing vertical "s" s
Fly fast, live slow
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 6:33 pm

Yeah, the 'ole days...not so bad, either.
I sometimes think that the more change there is, the more it remains the same.
 
pilotaydin
Posts: 2099
Joined: Tue Sep 07, 2004 12:30 am

RE: Backcourse/ ADF Questions

Thu Mar 03, 2005 7:33 pm

that website is kinda misleading...there is no signal on the localizer that is sent along the extended centerline, there are two lobes of transmissions, one is 90 Hz and the other is 150 Hz and these two lobes are interpreted by the a/c, depending on which signal is stonger, this will give u deviation from a position which receives equal strength from both lobes - this position is the centerline, the glideslope works in similar fashoin.
The only time there is too much fuel onboard, is when you're on fire!
 
OzLAME
Posts: 336
Joined: Thu Feb 17, 2005 8:40 am

RE: Backcourse/ ADF Questions

Fri Mar 04, 2005 8:34 pm

Quoting PhilSquares (reply 9):


Quoting PhilSquares (reply 7):
Maybe I'm missing something, but on a glass cockpit, you can build the approach in the FMS and fly it in LNAV. You could always use V/S to fly the descent profile.



That is quite true, but that is neither flying the front course or backcourse. You would be flying a Non-Precision Approach using a psudo-glideslope derived from VS and/or the published FMS/GPS Approach
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Backcourse/ ADF Questions

Sat Mar 05, 2005 12:22 am

With most, set the inbound front course, and fly to the diviation bar...correct sensing will be provided, inbound on the back course, as well.

I'm not sure I completely understand that statement. There are two types of systems and it doesn't really matter if you're flying glass or steam.

On one type, you dial in the reverse course to get normal "fly to the needle" sensing.

On the other type, you dial the front course, and select LOC backcourse (usually on the AFCS mode selector) to get normal "fly to the needle" sensing.

Either method will normally provide annunciation that you are flying the backcourse. Often using a "BC" annunciator.

The mechanical HSIs have an integral switch that turns the BC light on when you are tuned to a LOC frequency and have the course selector greater than 90 degrees from the airplane heading. The EFIS airplanes do it through software.
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Backcourse/ ADF Questions

Sat Mar 05, 2005 12:42 am

I have only used the Collins HSI's in large turbofan airliners to fly backcourse approaches, Airplay, so I can't really comment about other aircraft.
In these aircraft that I have flown (with the Collins units), the front course QDM is always selected, and correct sensing is automatically provided.
No separate annunciation was provided...it was up to the pilot flying to know where they were on the approach.

An interesting observation, from many years ago, might interest a few younger folks here.
Location...PanAmerican B707 non-visual simulator, SFO, circa 1973.
Individual under training... a Flight Engineer upgrading to First Officer.
Approach...backcourse approach to runway 11, OAK (possible then).

The trainee was hand flying this approach, using the flight director (backcourse mode), but instead of remembering that there was no glidepath, flew the sim right into the 'water' of SFO bay...whereupon the instructor (a very senior PanAm Captain) tossed a small cup of water on this guy, and mentioned....'hey sport, you just got wet, and no doubt killed a few passengers in the process.'
The other crew members had been told to keep quiet, to see just what this guy would do on his own.

Airline training is designed to keep the incidents/accidents in the simulator, where they should be, and is no picnic for new guys moving up the ladder, then or now.
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Backcourse/ ADF Questions

Sat Mar 05, 2005 12:50 am

Quoting KYIPpilot (reply 5):
Ahh, I remember now, thats right. I have only done one backcourse ever. Thanks!



Hey KYIP, come over to AZO. We've got one you can use.

2H4


Intentionally Left Blank
 
OzLAME
Posts: 336
Joined: Thu Feb 17, 2005 8:40 am

RE: Backcourse/ ADF Questions

Sat Mar 05, 2005 10:33 am

My background is GA so I have very rarely seen mechanical HSIs other than the Collins 331A or King KI 525, which are 3" instruments. They do not have space inside for automatic reversing of sense, hence the need for an external backcourse switch such as I described earlier. The Mitsu's I worked on had 331A HSIs and Bendix M-4 autopilots, neither of which could work out by themselves if the a/c was on a backcourse. Of course, you do get what you pay for and the HSI in a large turbofan could probably buy you an entire bug-smasher complete with a 3" HSI.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.

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