Question For The Experts

[klfrodo]

I’ve been stalking BA288 PHX to LHR because that’s my flight in a few months.

I don’t think this flight has ever departed PHX on time. It’s been close a few times but usually 30 minutes to a couple of hours late. This flight usually does arrive at LHR usually only 5 to 15 minutes late. Rarely more than an hour late.

 

My question: Does operations delay departure to coincide with predetermined landing slot schedule based on winds and weather on flight route?

[CruiserBruce]

Generally,  yes. The flight will have a landing slot. The plane will leave at whatever time gets the plane there to land in that slot, considering all factors like weather,  other traffic,  etc.

[Globaliser]

7 hours ago, klfrodo said:

My question: Does operations delay departure to coincide with predetermined landing slot schedule based on winds and weather on flight route?

 

This is very common, but it's also to do with making sure that there is sufficient operational capacity at the arrival airport to deal with the flight. There's no point having flights depart "on time" only to have them arrive (for example) an hour before the baggage handlers have arrived at work. Airlines have quite a lot of leeway about actual arrival times for the purposes of working out whether they've properly operated the slot. But operational constraints don't give you that much leeway: if your baggage handlers are rostered to start work at 7 am, they're unlikely to be keen to turn up early at short notice.

 

At Heathrow, I think that the strictest rules about slots concern night flights. There's a very limited number of flights that are permitted to land between 0432 and 0602, and airlines usually allocate these to specific flights. If your flight is not a quota flight, the airline's default position is that it simply can't land before 0602. So there's no point in it departing "on time" only to burn tons of fuel circling around London waiting for the magic hour when it's allowed to land. The same applies even if your flight is a quota flight but you would get to London before 0432. If such a situation develops during the course of the flight, the aircraft is often slowed significantly so as to delay its arrival.

 

The general public often treats "on time" departure as some sort of hallowed principle. But the only metric that really matters is whether arrival is on time.

[klfrodo]

3 hours ago, Globaliser said:

 

The general public often treats "on time" departure as some sort of hallowed principle. But the only metric that really matters is whether arrival is on time.

You're right. We do treat "On Time" as a hallowed principle. All our lives, being on time is beat into our heads. From a very early age, my parents beat into my head, not to be late to school or late to church, late to dinner, or late to work. The military taught me that that if I arrived to formation "On Time", I was 15 minutes late. The family trip to grandma's house for Christmas, Dad had an AIS departure time for the road trip. Oh Lordy, don't even think about being late for that one. Hurts just thinking about it.

The "general public" is not stupid about being late. The aviation industry just hasn't communicated to the "general public" how the industry works.

That's not to say that it is expected to throw out a series of PSA's about this information, however, there is a ton of programming out there about airport operations where this information could be shared. 

I'm 65 yo and traveled for business for 25 years. I'm today years old when I first thought about why some flights departures are delayed. My wake up schedule, my drive time schedule, my airport arrival were all scheduled around "On Time" departure. So Yes, I considered "On Time" departure as a hallowed ground.

However, I now have a better understanding of airline and airport operations. For that, I thank you.

[Globaliser]

2 hours ago, klfrodo said:

From a very early age, my parents beat into my head, not to be late to school or late to church, late to dinner, or late to work. The military taught me that that if I arrived to formation "On Time", I was 15 minutes late.

 

Interestingly, all of these are examples of the importance of on time arrival.

[GeezerCouple]

7 hours ago, Globaliser said:

...

At Heathrow, I think that the strictest rules about slots concern night flights. There's a very limited number of flights that are permitted to land between 0432 and 0602, and airlines usually allocate these to specific flights. If your flight is not a quota flight, the airline's default position is that it simply can't land before 0602. So there's no point in it departing "on time" only to burn tons of fuel circling around London waiting for the magic hour when it's allowed to land. The same applies even if your flight is a quota flight but you would get to London before 0432. If such a situation develops during the course of the flight, the aircraft is often slowed significantly so as to delay its arrival.

 

The general public often treats "on time" departure as some sort of hallowed principle. But the only metric that really matters is whether arrival is on time.

 

Okay, I'll bite!

I understand the situation about slots available, regardless of whether it's due to weather or staffing or whatever.

However, IF it's staffing and starting times/etc., shouldn't that be incorporated in the scheduled departure/arrival time?  Weather delays or snafus at the airport, yup, understand that.

 

But I'm intrigued:  What is special about "between 0432 and 0602"?

I knew there were night restrictions, but I definitely assumed they started well before 0432.

And also, what's with the "2".

 

Thanks!

 

Curious GC 😉 

[Globaliser]

25 minutes ago, GeezerCouple said:

However, IF it's staffing and starting times/etc., shouldn't that be incorporated in the scheduled departure/arrival time?

 

Staffing will be planned around what's needed for schedules. But actual flying time can be very different from what the schedule implies. Looking at my own non-stop flights, I see the following spreads:

• Bangkok to Heathrow between 10:53 and 13:33;
• Hong Kong to Heathrow between 12:25 and 14:43 (plus one outlier of 16:04 - a very unusual flight);
• JFK to Heathrow between 5:38 and 7:24 (excluding Concorde).

 

So if on any particular day departing on schedule means that you can't land at Heathrow, or you'll get there before the staff do, there's just no point departing on schedule.

 

36 minutes ago, GeezerCouple said:

But I'm intrigued:  What is special about "between 0432 and 0602"?

I knew there were night restrictions, but I definitely assumed they started well before 0432.

And also, what's with the "2".

 

These are noise-related restrictions at Heathrow. Although it's a little bit more complicated than this, the basic effect of the night flight regime is that flights can't land before 0602, except for a handful of flights that may land from 0432. These times are for actual landing times, not scheduled arrival times.

 

I've never manage to get an authoritative answer for the "2". But I suspect that this is because the lower that an approaching aircraft is, the more noise is experienced underneath it. They are particularly noisy in the last part of the approach because when flaps, slats and landing gear are extended, these produce a lot of additional aerodynamic noise, which on modern aircraft can be rather louder than engine noise. So the first landing may be at 0432 so that the noisiest part of the flight doesn't begin until about 0430 (and similarly for 0600, when the regular one-a-minute landing pattern begins).

[GeezerCouple]

3 minutes ago, Globaliser said:

...

These are noise-related restrictions at Heathrow. Although it's a little bit more complicated than this, the basic effect of the night flight regime is that flights can't land before 0602, except for a handful of flights that may land from 0432. These times are for actual landing times, not scheduled arrival times.

 

I've never manage to get an authoritative answer for the "2". But I suspect that this is because the lower that an approaching aircraft is, the more noise is experienced underneath it. They are particularly noisy in the last part of the approach because when flaps, slats and landing gear are extended, these produce a lot of additional aerodynamic noise, which on modern aircraft can be rather louder than engine noise. So the first landing may be at 0432 so that the noisiest part of the flight doesn't begin until about 0430 (and similarly for 0600, when the regular one-a-minute landing pattern begins).

[emphasis added]

 

Ah, thanks.  I misread what you had written as meaning that flights couldn't land *between* 

0432 and 0602, which seemed very odd indeed.

 

What time do the noise restrictions begin, and are they staggered at all, like for the flights that can land between 0432 and 0602?

 

Many thanks, as always.  The information you share with us is very much appreciated, and also interesting! 🙂

 

GC

[Globaliser]

13 hours ago, GeezerCouple said:

What time do the noise restrictions begin, and are they staggered at all, like for the flights that can land between 0432 and 0602?

 

There are noise restrictions all the time - for example, the oldest noisiest aircraft are basically not allowed to operate at Heathrow at all - but for most practical purposes the main restrictions start in the late evening and continue until 6.00 am. As you would expect, the most stringent restrictions are those that apply in the middle of the night, but they are slightly eased for landings from 4.30 am. And the rules do have provisions to allow for exceptional circumstances (for example, to try to clear backlogs after major disruption) and emergencies (if you have to make an emergency landing, Heathrow will always be open for you).