Ask The Pilot

[jb747]

With the express path and Crew lane at MEL being the same, I was talking to the flight crew of QF94 this morning to hear that the second officers bag was instead sent to BNE on QF16 and not MEL.

How often do crew have their checked items misplaced by the airline they work for?

As I haven't checked a bag in many years, it never happens to me. The reason I never check bags is that mine was misplaced on two consecutive trips! Overall rare, but it certainly happens.

 

[jb747]

On a trip across the Tasman yesterday I noticed the SOG on the display showed a speed of 1119 kph. This is the highest I can remember as usually it is normally in the mid to high 900's. Makes me ask "what is the fastest SOG a plane can go". Would have had a good tail wing I should think

The question should really be "how fast can the wind blow", as that's what is making the difference. 200 knot high level winds are not uncommon, and can be a great help if they are smooth and going the right way. Highest I can recall was around 715 knots (1325 kmh)...so with a TAS of around 495 knots that's a 220 knot wind.

Perhaps a more interesting question amongst pilots would be to ask the highest IAS ever seen. For me it's 640 knots. For Mirage/F18 people I'd expect about 750. F-111 possibly into the 800s. Airliners...330-370.

 

[Franky]

Perhaps a more interesting question amongst pilots would be to ask the highest IAS ever seen. For me it's 640 knots. For Mirage/F18 people I'd expect about 750. F-111 possibly into the 800s. Airliners...330-370.

Would that have been in the little Skyhawks you once flew, if not, how would they compare with the aircraft mentioned above?

 

[Melburnian1]

From what I can deduce from the large number of domestic flights that departed MEL, SYD or other ports but were unable to land in BNE mid evening (around 2100 hours) in BNE on Friday 7 July, the weather bureau may have failed to predict the severity of the fog as one forecast I recall merely said 'fog patches.'

Since I am not a meteorologist but gather that a fog's extent (geographical coverage) and severity is among their more highly challenging tasks (and they appear to be unable to always get the forecasting correct), how often does this happen that ATC gives clearance to take off for relatively short distance domestic flights because it is confident that flights should be able to land (in this case, at BNE) during the mid evening?

No Cookies | The Courier Mail

(If the paywall defeats you, heading that can be entered into Google is 'Brisbane weather: fog envelopes city' by Clare Armstrong and Tom Snowdon.)

Rightly or wrongly, most times one observes flights diverting in Australia it is during the morning hours from say 0800 to 1030 or so (but not identical for each location.) Is it relatively rare for our aviators when operating in Australia to experience mid evening fog that results in a flight having to divert?

 

[fresherbill]

Listening in on the Brisbane ATC chatter last night with the fog was interesting.


At one point, two international widebodies were readying for departure. One carrier sat on taxiway A for nearly an hour waiting for 550m of visibility to take off. Meanwhile, the second one pushed back, had a follow me car guide them to the runway (past the first carrier) and took off immediately saying they were good with 400m.


What decides the minimum acceptable visibility for takeoff - company policy, equipment capabilities, pilot discretion etc?

 

[mjt57]

Perhaps a more interesting question amongst pilots would be to ask the highest IAS ever seen. For me it's 640 knots. For Mirage/F18 people I'd expect about 750. F-111 possibly into the 800s. Airliners...330-370.

This bit I don't understand. According to this wiki article:

https://en.wikipedia.org/wiki/General_Dynamics_F-111_Aardvark#Overview

At altitude it could hit 2,655 km/h or around 1,400kts. At sea level it says 1,473 km/h or 795kts.

Is there a different (more accurate) way of interpreting this data?

 

[jb747]

Would that have been in the little Skyhawks you once flew, if not, how would they compare with the aircraft mentioned above?

640/1.2 mach was max speed for the Skyhawk. You could get about 1.1, but I never saw 1.2. 640 was pretty easy in a clean aircraft, though they normally carried external tanks (which were mostly empty) and which had their own more limiting speeds.

All aircraft are designed to perform well in particular parts of the envelope. The A4 worked best down relatively low, so high mach numbers were never a design goal. Even aircraft like the F111 may well have been subsonic with most stores loadings. Dogfighting against a Mirage, if he decided to turn with us...then we'd probably win!

 

[jb747]

This bit I don't understand. According to this wiki article:

https://en.wikipedia.org/wiki/General_Dynamics_F-111_Aardvark#Overview

At altitude it could hit 2,655 km/h or around 1,400kts. At sea level it says 1,473 km/h or 795kts.

Is there a different (more accurate) way of interpreting this data?

At sea level, the limiting speed is most likely the max allowed IAS. Because the air is thinner at altitude, that same IAS will result in a higher TAS as you climb. At FL400, TAS is approximately double the IAS. The limit speed at altitude would probably become mach number, but could be something more esoteric, like skin temperature.

 

[jb747]

Listening in on the Brisbane ATC chatter last night with the fog was interesting.

At one point, two international widebodies were readying for departure. One carrier sat on taxiway A for nearly an hour waiting for 550m of visibility to take off. Meanwhile, the second one pushed back, had a follow me car guide them to the runway (past the first carrier) and took off immediately saying they were good with 400m.

What decides the minimum acceptable visibility for takeoff - company policy, equipment capabilities, pilot discretion etc?

550 metres is the standard limit in Oz. To go below that, there are lots of requirements, mostly relating to the type and spacing of the runway lighting. There are also requirements with regard to the runway markings, edge lighting, the means by which the visibility is assessed, the number of points at which the vis is measured, and also crew training.

Our limit for Brisbane is 350m. In London our limit is 125m.

It requires continual training. A deviation from centreline in which you lose reference is a major problem...this is most likely to happen after an engine failure, which, of course starts with a big swing. The support you get from the right hand seat can be vitally important.

 

[jb747]

From what I can deduce from the large number of domestic flights that departed MEL, SYD or other ports but were unable to land in BNE mid evening (around 2100 hours) in BNE on Friday 7 July, the weather bureau may have failed to predict the severity of the fog as one forecast I recall merely said 'fog patches.'

Since I am not a meteorologist but gather that a fog's extent (geographical coverage) and severity is among their more highly challenging tasks (and they appear to be unable to always get the forecasting correct), how often does this happen that ATC gives clearance to take off for relatively short distance domestic flights because it is confident that flights should be able to land (in this case, at BNE) during the mid evening?

No Cookies | The Courier Mail

(If the paywall defeats you, heading that can be entered into Google is 'Brisbane weather: fog envelopes city' by Clare Armstrong and Tom Snowdon.)

Rightly or wrongly, most times one observes flights diverting in Australia it is during the morning hours from say 0800 to 1030 or so (but not identical for each location.) Is it relatively rare for our aviators when operating in Australia to experience mid evening fog that results in a flight having to divert?

You're right that fog is more common in the mornings, but it can, and does, happen at any time of the day.

I don't know that ATC have to have any confidence that you'll be able to land at your destination before issuing a take off clearance. They don't have operational control of the aircraft, and really just want to get it out of their airport. Subsequent landings or diversions belong to other ATC, the airline ops centres, and the flight crews themselves. Not all aircraft or crews have the same ability to operate in low vis conditions, and this is not up to ATC to assess.

 

[jb747]

This is relevant to the discussion about wind above, and also IAS/TAS. Taken this morning.

 

[petercr]

so that's a CAS of ~255kt at 39,980ft = 0.837 Mach = a TAS of 480kts and somewhere just north of Cobram?

 

[jb747]

so that's a CAS of ~255kt at 39,980ft = 0.837 Mach = a TAS of 480kts and somewhere just north of Cobram?

The display also shows that the FOs autopilot is flying the aircraft (AP2), and his altimeter would have been spot on 40,000 feet. Wind is 189 knots, and mostly crosswind from the right. 20 degrees of drift, and 101 knots taken off the TAS for a groundspeed of 379 knots. Position is 7 miles south of Parkes.

 

[mjt57]

What does the green line at roughly 5 to represent?

I had to read up on what "TAS' actually meant. There's a Wiki article that more or less explains it to my level of understanding.

 

[jb747]

What does the green line at roughly 5 to represent?

I had to read up on what "TAS' actually meant. There's a Wiki article that more or less explains it to my level of understanding.

There's a lot on those displays, and at the flick of a switch the ND (the right one) can be changed dramatically.

The green line you're looking at is an image of the FMC programmed track. In this case it goes from Parkes (pretty much under the aircraft symbol), to position POLSO, which is off the screen. The data at top right is showing next waypoint, distance to run, and eta. The display is called the ND or nav display, 'cos it's basically a map. Current position is at the bottom centre, and it aligns in the direction we are pointed (heading). The range rings in this case are separated by 20NM...the overall display being 80NM. There are many scales to choose from. The yellow bug next to the numerals '23', is the aircraft heading (currently 227º). The green diamond is showing the track..which is 206º, and it's aligned with the green track line because we are flying down that track. That's shown above the attitude indicator, by the green NAV, which means we're following an FMC track.

The two white needles (at 200º and 204º) are the tails of VOR 1 & 2. They should also be showing that 206º track, but as we've just overflown those aids they take a little time to settle down again.

Radar data is also displayed on the ND, but apart from one little blip at about 50 miles there's nothing being shown.

The lower part of the display is a vertical cut of radar data. In this case it's looking along the track, and if there were any radar returns their vertical profile would be shown. The green line here, is the aircraft's planned trajectory.

 

[Flying Fox]

On the left display, on the lower left hand corner there seems to be a cross section wing image. Does this represent flap & slat position (guess on my part)?

PS, thanks for the images. I found them fascinating.

 

[jb747]

On the left display, on the lower left hand corner there seems to be a cross section wing image. Does this represent flap & slat position (guess on my part)?

PS, thanks for the images. I found them fascinating.

Correct. It shows the selected settings, and the actual as the surfaces move. Spoilers also show up on the wing. If armed they go green, and if unstowed, the image reflects their actual position. You always have a look at the spoilers every now and then. When armed, they sit up about an inch at the trailing edge, to ensure no fouling with the flaps as they move. If you leave them armed, that rise will convert into substantial extra fuel burn. That was a gotcha when the aircraft first appeared.

The blank areas can also hold various messages (largely redundant), as well as pitch (on the ground) and rudder trim (if you've been moving it). Landing gear position also shows up there.

I'll get some pictures of the system showing other data.....

 

[flychrisfly]

The blank areas can also hold... pitch (on the ground)

Thanks for the info - very interesting!

How does pitch work as a concept on the ground? I'm perplexed! Or are we talking take off and landing?

 

[jb747]

Thanks for the info - very interesting!

How does pitch work as a concept on the ground? I'm perplexed! Or are we talking take off and landing?

Pitch trim. The standard setting is 39.5%. The tail will be moved to the correct position for take off automatically...as long as the setting is correct. It's part of the take off performance, and load sheet, data.

Vitally important for take off. Too little and you may not be able to rotate. Too much and you may not be able to stop the rotation. Airliners will give a warning if outside the normal trim range.

As long as you are in normal or alternate laws, the aircraft trims itself in pitch.

 

[flychrisfly]

Pitch trim. The standard setting is 39.5%.

Thanks, what is the setting a percentage of? As in, what does it mean?

Thanks again!