Ask The Pilot

Re: Now Boarding ... Chicken or Beef?

the limit would be the time taken for the IRSs to align.

What would be the reason that the IRS need to align to be able to fly the plane? Could it not be taken into the air flown visually?
 
Re: Now Boarding ... Chicken or Beef?

What would be the reason that the IRS need to align to be able to fly the plane? Could it not be taken into the air flown visually?

It truly isn't a Cessna.....

I'd hate to think what wouldn't work if you didn't let the IRS align. Direct law for a start.
 
Why does IRS take so long to align? I was under the belief that when you go to align the IRS you also enter in the current co-ords (either from the GPS or the lovely sign at the gate), why does it then take 10 minutes to align?
 
Why does IRS take so long to align? I was under the belief that when you go to align the IRS you also enter in the current co-ords (either from the GPS or the lovely sign at the gate), why does it then take 10 minutes to align?

It takes 10 minutes to assess the earths movement which becomes the baseline datum:

Alignment (1) IRS alignment consists of determining local vertical and initial heading. Both accelerometer and laser gyro inputs are used for alignment. The alignment computations use the basic premise that the only accelerations during alignment are due to the earth's gravity; the only motion during alignment is due to the earth's rotation. Accelerations due to gravity are always perpendicular to the earth's surface and thus define the local vertical. This local vertical is used to erect the attitude data so that it is accurately referenced to vertical. Initially, only a coarse vertical is established. Once vertical is established, the laser gyro sensed earth rate components are used to establish the heading of the airplane. As the alignment continues, both the vertical reference and the heading determinations are fine tuned for maximum accuracy.
(2) The orientation of the vertical axis of the attitude reference relative to the earth's surface is based on airplane position input to the IRU. The initial position entry can be made at any time during the alignment period. Earth rate sensing by the laser gyros allows the IRU to determine initial latitude. This gyro determined latitude is compared to the crew entered latitude. Crew entered longitude is compared to the last stored longitude. These comparisons must be favorable to complete the alignment period. During the alignment period all outputs of the IRU, except for present position, are set to NCD (No Computed Data). The minimum duration of the align mode is 10 minutes.

http://digilander.libero.it/andreatheone/irs.htm
 
It isn't just a navigation system, although it still provides that information (and is supplemented by GPS). It provides all of our attitude data. It also provides data to the FBW system that it uses to actually fly the aircraft.
 
Do you watch shows like Air Crash Investigation? And if so, do you watch while touching wood (no pun intended) and throwing salt over your left shoulder?
 
Do you watch shows like Air Crash Investigation? And if so, do you watch while touching wood (no pun intended) and throwing salt over your left shoulder?

Not really. They are dumbed down to such an incredible extent, and constantly repeat themselves for the millions of ads that are inserted that they're pretty useless. The actual reports are generally much better reading, and are readily available.
 
I bought the box set because its so dramatic recreation of events, great for a laugh.
My flatmate and me sit on the couch trying to work out whats real and whats not!
 
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Re: Now Boarding ... Chicken or Beef?

When the 380 was grounded, there's a break of about 7 weeks in my flying..but a sim every few days.

Thanks jb747 for these wonderful insights.

Just out of idle curiosity did you commute up from Melbourne each time or did you just stay in Sydney?
 
Re: Now Boarding ... Chicken or Beef?

Just out of idle curiosity did you commute up from Melbourne each time or did you just stay in Sydney?

A mix. Mostly I just commute, but I've got a room in a flat in Sydney, so I stay as required.
 
Re: Now Boarding ... Chicken or Beef?

Thanks jb747 :) And thanks for not laughing about the "key" thing :) I was expecting someone to make a joke like, "I can't fly today. I left the keys at home."

I suppose there's no phrase in the pilot / flying parlance equivalent to the driving expression, "Drive like you stole it."

Military trucks are similar. No keys. There's still a "key" which powers the electrics (and starter) but you cant actually remove it. And some have air start so they don't need to rely on electricity at all. The exception are civilian vehicles that are "mil-specced" (i.e. painted green), but they only used for non-tac scenarios.

It would be a bit inconvenient if you had to bug out really quickly and someone had removed the keys. Or locked the doors.

[video=youtube;BPiSb3Py2x4]http://www.youtube.com/watch?v=BPiSb3Py2x4&feature=player_detailpage[/video]
 
Re: Now Boarding ... Chicken or Beef?

Hi JB,

On a recent flight from Helsinki our aircraft was deiced prior to push back. When the flaps were extended for take off I noticed large chunks of ice still on them. Is it safe to depart like this?

Ian
 
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Not sure if this has been asked but a QF flight last week tail striked at SYD.

How hard would it be to make that mistake or is it something that happens regularly and we just don't hear about it unless it is a QF flight.
 
Re: Now Boarding ... Chicken or Beef?

On a recent flight from Helsinki our aircraft was deiced prior to push back. When the flaps were extended for take off I noticed large chunks of ice still on them. Is it safe to depart like this?

Rather hard to say without actually seeing it. But, if the ice came out of the flap tracks/cracks during extension, I doubt that it would be too much of an issue. Still undesirable though.
 
Re: Now Boarding ... Chicken or Beef?

For a normal passenger trip, it takes about 45 minutes to do all of the things that need doing. But, if I was trying to steal it, and skipped just about everything, the limit would be the time taken for the IRSs to align. So, perhaps 10 minutes.

...

No...but there's a lot of security to get past before you'll get near the aircraft.
Finding reverse gear to back out of the gate might be a bit tricky, too.
 
Not sure if this has been asked but a QF flight last week tail striked at SYD.

How hard would it be to make that mistake or is it something that happens regularly and we just don't hear about it unless it is a QF flight.

Some aircraft are quite prone to tail strikes, and the 767-300 would have to be near the top of the list.

There is a big difference though, between a tail strike, and a tail scrape.

In a NORMAL 767 take off, the tail gets to 18-24 inches off the runway. Not much clearance, and if the rotation rate is even slightly faster than normal, you'll quickly reduce that clearance. Note that the issue is not too steep a pitch attitude. 767s are ALWAYS rotated to an attitude that will cause a strike if you achieve it too quickly.

From memory, liftoff happened at about 8º, and the skid would hit at 12º....but, the target attitude for a 767 takeoff will be around 20º. It tends to be more of an issue in gusty conditions, where it's harder to keep that constant rotation rate, and increasing climb rate. For instance, a 10 knot loss of airspeed just after rotate started could easily cause the climb rate to slow and get out of synch with the rotation.

Is it a problem? Contrary to what the media will make of it, most likely not. Boeing are well aware that the 767-300 has this issue, so it is equipped with a tail 'bumper' or skid, that extends and retracts with the landing gear. So, any contact will not be with the fuselage, but with the skid, and all that will happen is that the neoprene tip will lose some of its paint (and the paint condition was always carefully inspected during to preflight).

Other aircraft types, without benefit of this bumper will scrape the fuselage, and of course the aluminium skin doesn't react well to that.

Tail scrapes are the more extreme end of the scale, but are not normally caused by rapid rotation, but rather by incorrect data calculations. Emirates in Melbourne, and Singair in Auckland are two very good examples of this. In each case, the aircraft was rotated until the tail firmly hit the ground, and it was then held there until it accelerated enough to fly. They're both very damaging, and extremely dangerous.
2003 03 13 112111 (00008).jpg
 
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