I believe the questions that need to be answered are :
1) Is it confirmed the 3 aircrafts actually declared a mayday fuel or did they opt for a minimum fuel / PAN call and ATC has asked them to squawk 7700 for their own London Area Ops ?
2) In case of a multiple mayday call by 3 aircrafts diverting, what is the root cause ?

Being clear on the above could be helpful.

Three possible areas of consideration ...
1 Single seater - self-concerned and relatively unrestricted
2. Pax conveyor with commercial and other limitations
3. ATC controller(s) with multi inputs, coordination (traffic) problems.
The question is posed, perhaps unsurprisingly, by 1.

How long does it take for a controller to organise one diversion??? That time can take you from no emergency to MAYDAY pretty easily. I did STAC at Swanwick last year and a figure was quoted, I just can't remember whether it was 10 or 15 mins...

Part of the problem in the south east of the UK is that if you need to divert to your primary flight plan diversion, but they won’t accept you, ATC end up saying “you know what you need to do”. We shouldn’t be having to call MAYDAY just to play the game to get to our nominated diversion and it goes somewhat against the convention of the standard phraseology regarding minimum fuel states. It’s not ATC’s fault and they’re always excellent. These days I always carry fuel to cover a non London alternate. It’s just not worth he stress.

It can easily be that long. We have to get approval from the airport before we can send you there and that's what takes the time.

For the actual ATC side of it, it's pretty easy. It involves us putting a new route into the computer to make sure the right sectors get your details, coordinating with the next sector if required and then telling you the route, except you probably already know that, but we have to tell you anyway

AFAIK only 1 a/c declared MAYDAY, however 3 others squawked 7700, not at the request of ATC. NONE declared PAN.

As for DIVs it is not uncommon for a named alternate to refuse the DIV, particularly LTMA airports on bad weather days/peak hours. With multiple DIVs at any one time workload becomes very high trying to find a suitable alternative which will accept the DIV as the request routes Aircraft - Terminal Controller/Area Controller - Supervisor - TWR - Airfield OPS and then back again which can (at times) take a lot of time.
Capacity restraints within LTMA airports make the current DIV process unfit for purpose and safety compromising which was realised during the recent storms. This is something the CAA should seriously look at.

and what happens as soon as we say the magic word? Permish goes out of the window. I guess this is where these guys got to. As soon as one called it, I bet the other two piped up pretty quickly.

The reality is not everyone is operating to this level of fuel, due to the range of flight durations and conditions encountered enroute. there is therefore a distribution of endurance as people hit the stack.

Problem is, there are the unknown unknowns (not talking about your prob 30 tempos that turn out far worse) like drones or security events in the terminal. Statistical contingency can’t account for this, neither can 5%/5 mins holding on a short sector.

Airlines have an overriding responsibility for safety, but also consider operational efficiency.sometimes benign conditions together with modern commercial, very accurate planning systems, when a “black swan” event occurs can really screw things up. We don’t use string on a map, fold lines or rules of thumb.

anyhow, something must be working. When was the last time aircraft were falling from the skies with dry tanks? What helps is London Air Traffic being literally awesome and by far the best controllers we work with. East coast USA? Bad weather at destination? Give me another two tonnes minimum.

Military flying generally involved filling the tanks or going up to MTOW as you need the operational flexibility it gives in theatre with turd atc and no proper support on the ground, not to mention “the fog”, plus operating with a vastly inexperienced (but well meaning) operational control structure. The commercial world has comparatively a far more benign operational environment, with far greater comms capability and very experienced people on the ground (multi decade experience) with data from acars and lacking a lot of the fog of war. This means you can SAFELY plan to lower margins of fuel.

If you divert from overhead destination with your normal reserves, you should be able to fly to the alternate and land still with 'final reserve fuel' on board; there is no need to declare an emergency of any sort. If you are go below final reserve fuel, you must declare a Mayday.

If you set off on a diversion and have to declare Mayday straight away, then something has gone wrong. Either the crew held for too long and have started the diversion below the normal reserves or the fuel planning was wrong, by which I mean maybe an unrealistic route from destination to alternate was catered for.

Couple of scenarios. Previously issued ET becomes invalid as it’s taking longer to clear the runway. With an ET you can hold below diversion fuel.

airspace congestion led to longer routing.

aircraft told of ET at diversion, or in organising diversion, that meant they would be landing with below reserves level of fuel.

Say the magic word, all stops are pulled, having been in a similar situation in the Middle East with an intransigent host nation trying to make a political point resulting in us having no diversion option, other than the country we were filed to land in.

Would You really burn your alternate fuel in the hold while waiting the runway to be cleared / inspected on an airport without independent runway OPS ?

I guess you didn't read the thread. First of all, no, you do not declare mayday only once you are below final reserve fuel, you declare it as soon as you are reasonably sure that you will land with less than final reserve fuel. Which can be at a time where you are still quite a bit above final reserve fuel. Not to mention, at some point the low fuel warning of the aircraft will come on, that is a LAND ASAP amber indication which could be interpreted as reason for a PAN or MAYDAY depending on how you are trained.

And as has been explained in here, you fly to your destination, you do the approach, missed approach, decide straight away you want to divert, and ATC tells you to stand by for 15 to 20 minutes. That is an amount of time that is not included in your alternate fuel. You are straight away in a mayday situation as you will land below final reserve fuel. Of course, there could be contingency fuel, if that hasn't been used before, but that is at minimum only 5 minutes worth of holding. You still have to wait another 10 to 15 minutes until ATC has sorted out the approval, routing and so on. Still a mayday situation.

Of course, we could always take those 15 minutes as extra fuel. And personally i like to take 20 minutes into the london TMA simply because they advise us that "no delay" means up to 20 minutes of holding. But during a low season day to your homebase in benign weather? Probably not.

Agree on the above. I believe that all those kind of considerations should be embedded in the fuel planning regulations at EASA level. If I have the legal amount of fuel at all times and take my decisions accordingly I can't end up in an emergency because TMAs are busy and ATCs need to coordinate diversions and so on. I mean if that is always case it is perfectly fine and understandable given the amount of traffic nowadays, but the rules should take it into account and EASA should intervene through the appropriate channels to ensure Operators plan fuel accordingly.

Multiple simultaneous fuel emergencies declared?

Sounds to me like a systemic aspect exists here.

Company policy (aka local training department) browbeating crew to fly with minimum fuel and some delay occurring (this pressure has been a persistent problem in several companies as we well know) - suddenly several of that company's aircraft are trapped in the hold and crews begin sweating. All know what they ought to do but human nature being what it is hold off on the hope of a reprieve in another three or four minutes to save the interview and all the paperwork - and possible pointed fingers...finally someone has the sense to do what everyone is thinking and the dam bursts; there is a relieved cascade of MAYDAYS from crews who are thinking, well, at least it isn't just us...

Just surmise you understand...

If I have been given an ET off the hold by ATC, and I think its realistic, yep. I would have a brief discussion with ATC emphasizing the situation to ATC though, together with any margin above declaring a Mayday.

That is also what everybody else would be doing in that exact same position unless they have loads of extra fuel for no reason. Having multiple airplanes declaring mayday in the same TMA due to fuel on a fair weather day is not normal (nor it would be even on a stormy day). As I have written in another post, it is fine if ATC takes some time to coordinate diversion / routings, just highlight it to regulators / operators so that everybody can plan accordingly. No pun intended to the specific airline, they fully abide by the rules.

You wont get an EAT if runway is closed, it’s delay not determined.
would you really plan your fuel on the basis of an estimate of how long it was going to take to remove a stricken aircraft or for a concrete patch to dry?

was that the reason for the closure? No, of course not. But if it’s for an extended runway inspection due to a shedded tyre, yes I would. It’s all context. This job rarely is black and white. That’s the difference between a GA enthusiast and a professional pilot.

A small patch of runway break up, resulting debris and subsequent quick dry patch, I believe was the reason.

It would still be delay not determined if the reason was to allow someone to drive the length of the runway picking up various sized and amounts of shredded rubber for obvious reasons.

The only times I’ve diverted from LGW when the runway was closed, the response from ATC went along the lines of.. LTN is full, STN and BHX will accept you if you declare an emergency, there is space at EMA or the next available airport is LPL... not sure if this is relevant to the OP but as has been said, with the flow rate into LGW, when the runway shuts, the surrounding airports fill up very quickly.