To divert or not to divert?
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From: Near SOU
To divert or not to divert?
Firstly I apologise if this is a daft question, but an experience some years ago has always made me wonder about diverting and who makes the final decision to divert. The tragic events aboard the Singapore flight brought it back into my mind.
I am not a nervous flyer by any means, but one flight back in 2008 came very close to stopping me flying ever again.
My route was Manchester - CDG - Hong Kong aboard an Air France A340 for the longhaul sector. The plane was half empty, beautifully smooth flight. As we reached the halfway point the pilot made an announcement that we may have to divert due to the tail end of a typhoon that was slower to shift that had been expected. He apologised for the inconvenience and would update us later in the flight.
No further announcements came and we started to descend, I assumed that all was fine and having a window seat I has happily watching the world go by. Seatbelt signs came on and another announcement to the effect that we had been granted permission to land at Hong Kong but that there would be some weather so keep belted up.
There then came a sound that I had never heard before (or since). The sound was akin to having several truckloads of pea gravel being dropped from a great height on the roof of the fuselage. Peering out the window it was a full on lightning display, the sound of the thunder plus pea gravel was terrifying. I looked at the display on the back of the seat infront and we were still way over 20k feet up...subconsciously tightening the seatbelt, knuckles going a little white. By the time we were only about 45 minutes out, we had pea gravel, thunder, swaying in the wind, bouncing about, lightning....and the occasional scream from other passengers.
Finally we touched earth at Hong Kong, the pea gravel was still hammering the plane and now we had a ruddy great bow wave and water being flung in all directions (I was in a seat on the wing and I was transfixed to the waterworks display as we slowed down). We taxied to the gate and another announcement from the cockpit, a little shaky this time, apologising for the poor conditions etc and please stay belted til we arrive at the gate. Once at the gate there was a plane load of collective "thank heck for that" or words to that effect. Once everyone was off the plane and started making our way to passport control, the authorities stated - with a smile - that we were the last flight since the airport was now closed due to the weather.
When this sort of thing happens, who takes the decision to divert...is it the pilot or is it ATC?
A question for the pilots here, if you were in this situation and you knew that the destination airport was experiencing extreme weather at the halfway point, would you take the alternative destination or would you continue as our flight did?
Just curious.
I am not a nervous flyer by any means, but one flight back in 2008 came very close to stopping me flying ever again.
My route was Manchester - CDG - Hong Kong aboard an Air France A340 for the longhaul sector. The plane was half empty, beautifully smooth flight. As we reached the halfway point the pilot made an announcement that we may have to divert due to the tail end of a typhoon that was slower to shift that had been expected. He apologised for the inconvenience and would update us later in the flight.
No further announcements came and we started to descend, I assumed that all was fine and having a window seat I has happily watching the world go by. Seatbelt signs came on and another announcement to the effect that we had been granted permission to land at Hong Kong but that there would be some weather so keep belted up.
There then came a sound that I had never heard before (or since). The sound was akin to having several truckloads of pea gravel being dropped from a great height on the roof of the fuselage. Peering out the window it was a full on lightning display, the sound of the thunder plus pea gravel was terrifying. I looked at the display on the back of the seat infront and we were still way over 20k feet up...subconsciously tightening the seatbelt, knuckles going a little white. By the time we were only about 45 minutes out, we had pea gravel, thunder, swaying in the wind, bouncing about, lightning....and the occasional scream from other passengers.
Finally we touched earth at Hong Kong, the pea gravel was still hammering the plane and now we had a ruddy great bow wave and water being flung in all directions (I was in a seat on the wing and I was transfixed to the waterworks display as we slowed down). We taxied to the gate and another announcement from the cockpit, a little shaky this time, apologising for the poor conditions etc and please stay belted til we arrive at the gate. Once at the gate there was a plane load of collective "thank heck for that" or words to that effect. Once everyone was off the plane and started making our way to passport control, the authorities stated - with a smile - that we were the last flight since the airport was now closed due to the weather.
When this sort of thing happens, who takes the decision to divert...is it the pilot or is it ATC?
A question for the pilots here, if you were in this situation and you knew that the destination airport was experiencing extreme weather at the halfway point, would you take the alternative destination or would you continue as our flight did?
Just curious.
Joined: Feb 2003
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From: Brighton
There are many considerations: among the prime ones are weather at destination and at the alternate (including forecast changes in the relevant timescale), together with how much excess fuel you have to hold before making a diversion. Other than for US airlines, the decision is normally made by the captain, though sometimes the airline's ops room may give an instruction. In the US, airline despatchers and the airline ops rooms exercise much more detailed control over flights than is the case elsewhere, so they may well call the shots. ATC does not have all the relevant info, such as fuel endurance (though sometimes they will ask), crew duty time considerations, or why particular alternates are nominated. ATC also does not normally declare "airport closed" - usually it's up to the captain to evaluate whether the conditions are within limits for him, his crew, and his aircraft, given the state of the weather, landing aids, runways, and so on.
Last edited by kenparry; 31st May 2024 at 13:36.
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From: UK and Italy
I'd be interested in statistics and/or pilots' anecdotal experience of which aeroports experience the most diversions. CPT and MXP are two that seem particularly bad to me, but of course as a pax I don't fly anything like the number of sectors people at the pointy end do. I used to actively avoid MXP in favour of LIN when I commuted weekly LHR-Milan.
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From: Ferrara
N Italian airports can have shockingly bad weather - Milan has been a bad spot for years and last month we flew into Florence and it was dreadful - low cloud, rain, mist.............
IIRC one of the drivers for developing Autoland for Tridents were GLA, LHR and Milan
IIRC one of the drivers for developing Autoland for Tridents were GLA, LHR and Milan
Joined: Aug 2008
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From: UK
The “pea gravel” sound is typical of heavy rain, ie large drops. Ironically I would imagine this would be louder in the cabin at lower (approach) speeds when there’s more vertical component to it. Hail has a deeper sound and is of more concern as it does serious damage at higher speeds.
I’d also add that snow is a more difficult diversion call, especially at single runway airports where they have to close for ploughing (plowing to the yanks). Fortunately the Canadians and Scandi airports are experts at providing good info to approaching flights for decision making. The Brits not so much. Landing in falling snow on a recently ploughed runway isn’t a big deal unless there’s a crosswind, which is disorientating and can affect directional control if it gets slippery.
I’d also add that snow is a more difficult diversion call, especially at single runway airports where they have to close for ploughing (plowing to the yanks). Fortunately the Canadians and Scandi airports are experts at providing good info to approaching flights for decision making. The Brits not so much. Landing in falling snow on a recently ploughed runway isn’t a big deal unless there’s a crosswind, which is disorientating and can affect directional control if it gets slippery.
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My thanks to the Professional Pilots who took the time to give considered and detailed replies. Also to BonnieLass for a timely question that many must be asking. Despite all modern equipment thought up by the Boffins - the planet will continue to ignore us and do its own thing.
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From: GA, USA
I believe in the case of HongKong that the airport authorities will close the airport when the weather deteriorates to a certain level.
Roads and bridges will be closed and eventually the airport.
ATC doesn’t make this decision but they will obviously communicate it.
Someone will decide which plane on the arrival procedure is the last one to be authorized to land.
Roads and bridges will be closed and eventually the airport.
ATC doesn’t make this decision but they will obviously communicate it.
Someone will decide which plane on the arrival procedure is the last one to be authorized to land.
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From: UK and Italy
I guess I've been unlucky. I always seem to arrive when the tablecloth has come off Table Mountain and settled with unerring accuracy on the aeroport. Mind you, I've not been there since the 1990s.
Joined: Aug 2008
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From: UK
I’d say most diversions are caused either by airport closures (eg power failure, snow, flooding, politics) or visibility below limits. Every runway and its approach type (ILS, RNAV, VOR, circling etc) has a promulgated visibility limit. Even autolands have restrictions.
If the (usually automatically measured) visibility is less than the limit then you simply aren’t allowed to complete the approach (there are specific rules) so the decision is made for you.
There will also be company and aircraft manufacturer’s limits for eg crosswind component and pilot qualifications.
If the (usually automatically measured) visibility is less than the limit then you simply aren’t allowed to complete the approach (there are specific rules) so the decision is made for you.
There will also be company and aircraft manufacturer’s limits for eg crosswind component and pilot qualifications.
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From: NL
A question from the OP which I believe has not been answered is whether ATC or the pilot makes the decision to divert. ATC will never make that decision. ATC will of course inform the crew when their destination airport is closed and would then ask for their intentions It is not ATC's decision when and where they should divert. The crew may still elect to continue to their destination and wait it out while legal fuel reserves permit. The captain is ultimately responsible, although he may liaise with company operations.
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From: Asia
The Captain has the final decision and a number of alternate airports are provided in the flight plan. These are usually given in order of company preference. In the event of major disruption, ATC may assign division airports to aircraft as it may not be possible for a nearby airport to cope with the sudden arrival of a large number of aircraft, this often happens in China.
In the event of a technical problem, the airline may ask the pilot to divert to a suitable airport where maintenance facilities are available rather than continue to destination.
The pilot in command always has final authority and may declare an emergency if the situation requires it. Once on the ground he must then justify his decision to various parties, including his company, national civil aviation authority and the authorities of the country he is in at the time. Legitimate reasons and good judgment are expected and will be supported.
In the event of a technical problem, the airline may ask the pilot to divert to a suitable airport where maintenance facilities are available rather than continue to destination.
The pilot in command always has final authority and may declare an emergency if the situation requires it. Once on the ground he must then justify his decision to various parties, including his company, national civil aviation authority and the authorities of the country he is in at the time. Legitimate reasons and good judgment are expected and will be supported.
