How much time can jet planes make up?

[Mark11]

Waiting for my mum... Flight dj437 was 37 mins late leaving Adelaide... And only 18 mins late landing in Sydney ....

 

I wonder how fast they could do it if they went 100%?

 

 

[Ultralights]

tail winds? most delays in Oz are lack of ATC staff....

 

 

[Patrick Normoyle]

That's a bit harsh, as a current ATC I have a different take on it. We can offer a variety of time saving tools, climb higher to get better winds that we advise them of, direct tracking, high speed climb and descents. There are a lot of ways to get you there that bit quicker or slower. I don't disagree with the staffing issue, we are very short staffed and have been for a good 5 years or more.

 

 

[Sapphire]

Waiting for my mum... Flight dj437 was 37 mins late leaving Adelaide... And only 18 mins late landing in Sydney ....I wonder how fast they could do it if they went 100%?

I think if a plane leaves on scheduled time it arrives early based on it's schedule. Therefore it can leave late and still arrive on time. The last time I returned from Los Angeles we had to wait about 20 minutes in the plane or we would have arrived Sydney before the cerfew. They said it was cheaper to wait than circle Sydney for 20 minutes.

 

 

[facthunter]

The biggest factor is winds at cruise level. A Jet aircraft at the optimim cruise altitude cannot go faster or slower because it will get to a high or low speed stall with a speed variation of about 15 knots as a percentage of about 480 knots Average TAS, this is not significant as a consideration. Nev

 

 

[Old Koreelah]

The biggest factor is winds at cruise level. A Jet aircraft at the optimim cruise altitude cannot go faster or slower because it will get to a high or low speed stall with a speed variation of about 15 knots as a percentage of about 480 knots Average TAS, this is not significant as a consideration. Nev

I have read (perhaps on this forum) that a civil jet transport at cruise level and speed is just a smidgen above stall, given the thin air and reduced wing geometry. There is apparently only a small speed margin to operate in. Has anyone more concrete info?

 

 

[Gentreau]

There's some more detail here: http://en.wikipedia.org/wiki/Coffin_corner_(aviation)

 

 

[flyvulcan]

Old Koreelah,

 

You are correct, under certain conditions, the allowable speed range can be quite small, or indeed the high and low speed limits could be the same figure. However, most pilots avoid the situation of flying with such a small margin. Normally, the only time most would consider this practise is when flying for range, i.e. fuel is critical.

 

By way of explanation, the upper limit of the speed range for a typical jet is set by the manufacturer and is normally expressed as either an IAS or Mach Number. The high speed limit is set for any number of considerations including down low, windscreen/birdstrike limits, up a little higher it may be structural and at high level, it could be limited by compressibility or critical mach number (where airflow at some point on the wing is supersonic). G loading can effect critical mach number (an increased g loading increases the speed of the airflow over the upper surface of the wing, potentially making it supersonic) so a margin has to be allowed at high mach numbers to prevent reaching Mcrit during turns, in turbulence etc. when the aircraft might experience increased g loading.

 

The low speed limit is essentially the conventional stall as we all know it.

 

Now a typical airliner (say an A320) might have a clean stall of around 160kias near sea level but this increases with altitude and of course, with increasing weight. Up at 39000' and at the maximum weight to achieve that altitude, there may only be a 20 knot (or less) indicated split between the high speed limit and the low speed stall. On other aircraft, this operating range can be even smaller, down to just a few knots which means that any sort of disturbance could put the aircraft over/under the limits, i.e. if flying into a cloud that is cooler than the surrounding air mass, the mach number would increase momentarily putting the speed over the upper limit. Conversely, flying into some windshear where 10 knots is lost could put the speed under the low speed stall speed.

 

This situation is normally avoided by flying at a lower altitude where the margin is greater and waiting until enough fuel has been burnt off (so weight is reduced) before climbing to the next cruise altitude where a safe (or comfortable) margin would then exist.

 

I hope this brief explanation helps.

 

With respect to "making up time" in a jet, on a short sector (say under 2 hours), there is little scope to make up time. Typically, cruise speed can be increased by around 2% (so maybe a 4 minute saving over 2 hours) and a high speed climb/descent might save another 2 minutes. Selecting a cruise level that gives the best groundspeed (so TAS/wind combo), combined with direct tracking and traffic holding avoidance (ATC assisted) can help with making up time, but again, over a short sector, not much can be done. Over longer sectors, the percentage improvements remain the same but because of the length of the sector, a significant number of minutes can be "made up" (normally at the expense of fuel though which airlines are not that keen on).

 

Cheers,

 

Dave

 

 

[Mark11]

Dave,

 

Thanks for the explanation...

 

I thought that DJ437 did very well and I thought it was just a case of airlines electing to burn more fuel to reclaim schedule which might be cheaper than any fines for being late...

 

Learnt alot! Thanks

 

 

[shags_j]

tail winds? most delays in Oz are lack of ATC staff....

How on earth did you come to this conclusion?

Lack of staff has nothing to do with it. It is usually due to lack of gate time, or congestion. Any aircraft coming to brisbane airport knows it is going to have a delay, due solely to one runway and limited gates.

 

 

[Gentreau]

....Any aircraft coming to brisbane airport knows it is going to have a delay, ......

Aircraft knowing about delays, blimey those onboard computers are getting THAT intelligent ??

 

 

[Sapphire]

How on earth did you come to this conclusion?Lack of staff has nothing to do with it. It is usually due to lack of gate time, or congestion. Any aircraft coming to brisbane airport knows it is going to have a delay, due solely to one runway and limited gates.

 

Guess that makes sense. The plane is going to keep coming regardless if anyone is there or not.

 

 

[Guest Andys@coffs]

Dave,Thanks for the explanation...

I thought that DJ437 did very well and I thought it was just a case of airlines electing to burn more fuel to reclaim schedule which might be cheaper than any fines for being late...

 

Learnt alot! Thanks

Lets talk about another practical reality....... assuming an exactly the same crusing speed through the air (so not GS) flights from Adelaide to Sydney (W to E) will likely be early and flights from Sydent to Adelaide (E to W) will likely be late...... Our weather patterns move west to east..... As an ex Adelaidian It is most often the case that its the same plane that arrives from Syd that then immediately returns. so on purley E-W and the W-E whats lost one way is then gained in the return......

 

With Virgin at present in Syd at least, the majority of time lost is siting near the terminal waiting for a gate to free up, there are times when the que to dock can be 3-4 deep......Ive had the odd altercation with Hosties over turning on my ebook while waiting.......ebooks must be turned off...but a mobile is OK....<sigh> I always suggest that there isnt much chance of the pilot getting lost in the last 100m so we need not worry about our Nav equipment....but then end up turning it off...not worth the agrevation of having to explain to the AFP when we finaly extract ourselves from the que.....

 

Andy

 

EDIT: actuial the whole E to W think is an oversimplification........Lower half or Au its true but rless so, perhaps even reversed for the upper 1/2 of Au. Its why anyone driving a lighty around Australia normally doe it antclockwise so as to be more likely to have tailwinds than headwinds

 

 

[dazza 38]

I was surprised yesterday, we left Roma 1 minute late, landed at Brissy about 4 minutes late. Normally due to the current problems at Brissy the aircraft outbound to Roma (the one we use on the return leg) normally leaves brissy 10 to 15 minutes late.

 

 

[facthunter]

Soory Andy what you loose one way you do not make up on the other. The best situation is when there is NO wind. Any other and you total trip time will be more.

 

Jet stream winds are very strong getting to 220 knots frequently. They are at the cruising altitudes that jets use but there can be areas of turbulence at their edges. If you are at your maximum cruise level "coffin corner" or near it, you don't want turbulence.

 

Getting a "slot" is what holds planes up and the need for specific separation standards to be maintained limits the number of planes a system can handle. Some ATC systems use reduced separation and use the " visual" capability more. This is a safety issue. Even if you slow them down or have them in a holding pattern at some stage they still all have to come over the fence. Jets used to descend at much higher speed than they do today, so for many reasons trip times have increased over the same distances. TAS hasn't changed much since the B707. Nev

 

 

[Sapphire]

I read about a flight from Mexico to New York that was delayed with fatal consequences. The captain couldn't understand english so the co-pilot handled the radio:dizzy: They were endlessly diverted by changing ATC shifts etc to the point they were running out of fuel. Their terminology to convey this message was ambiguous and ATC never realized the the situation untill the a/c crashed waiting for a landing clearance. True story.

 

 

[eightyknots]

When I flew from New Zealand to Sydney recently, I was surprised by the amount of headwind that the Airbus encountered on the way. (see picture below). Despite the 135 km/h (73 knot) headwind, the plane still arrived 5 minutes early.

 

I'm glad I haven't encountered headwinds of such magnitude in the Piper Cub (yet).

 

 

 

[Sapphire]

Wonder what that little kink in the track is for. Maybe a bit of sight seeing on the way-happened to me flying LA to Vancouver. The pilot even wanted to circle Mt St. Helens but ATC said we would loose our slot.

 

 

[Guernsey]

When I flew from New Zealand to Sydney recently, I was surprised by the amount of headwind that the Airbus encountered on the way. (see picture below). Despite the 135 km/h (73 knot) headwind, the plane still arrived 5 minutes early.That's because the earth was rotating towards you so Sydney arrived quicker than if the world stood still.

 

Alan.

[facthunter]

If you get very strong headwinds at height, sometimes it pays to use a considerably lower altitude, if the head winds reduce.. Depends on the gain in groundspeed verses the increase in fuel flow. Once you are down a bit lower you have a bigger range of cruising speeds. In a strong headwind a faster cruise is better. It works foe U/L's too. The longer you are in the air the longer the wind is blowing you back. Nev

 

 

[Sapphire]

That's because the earth was rotating towards you so Sydney arrived quicker than if the world stood still.

 

 

 

[eightyknots]

That's because the earth was rotating towards you so Sydney arrived quicker than if the world stood still. Alan.

 

That's because the earth was rotating towards you so Sydney arrived quicker than if the world stood still.

 

Does that mean that all I need to do next time is buy a helicopter and hover and just wait for Sydney to catch up?

 

 

[Sapphire]

Does that mean that all I need to do next time is buy a helicopter and hover and just wait for Sydney to catch up?

 

 

[eightyknots]

Wonder what that little kink in the track is for. Maybe a bit of sight seeing on the way-happened to me flying LA to Vancouver. The pilot even wanted to circle Mt St. Helens but ATC said we would loose our slot.

I think they were looking for an island that has been on the map for over a century but is not easily visible from the air. Last week they proved that it doesn't exist

 

 

[Sapphire]

I think they were looking for an island that has been on the map for over a century but is not easily visible from the air. Last week they proved that it doesn't exist

 

Yeah, Tasmania