Was there still fuel on board?
Yes.
Did the engines flame out?
Also yes.
How and why? 👀
That’s probably the most confusing thing about the Glasgow helicopter crash to those who don’t fly the EC135 (which includes us).
On 29 November 2013, a police EC135 crashed through the roof of the Clutha Vaults pub in Glasgow, claiming the lives of ten people.
Normally, if you heard that both engines had stopped, you’d probably assume the helicopter had run out of fuel.
Double engine flameout ➡️ Reasonable assumption.
Except that’s not exactly true here.
When investigators examined the wreckage, they found around 76 kg of usable fuel still inside the aircraft.
So how do you lose both engines… when there’s still fuel on board?
Let’s break it down.
💥 Accident Overview
The EC135 had spent the evening carrying out routine police surveillance tasks around Glasgow and Edinburgh.
We have onboard:
🔸 1 experienced pilot
🔸 2 police observers
After completing their final tasking, the crew turned back towards Glasgow City Heliport.
Home was only a few minutes away, but things started to unravel.
The helicopter generated multiple LOW FUEL warnings on both engines.
Each warning was acknowledged, and eventually both remained illuminated.
According to the EC135 checklist, the helicopter should have landed within 10 minutes.
But that didn’t happen.
Around 2.7 nautical miles from the heliport, the right engine flamed out.
Thirty-two seconds later, the left engine did the same.
With both engines flamed out, the RADALT and steerable landing light were unpowered.
Unfortunately, the helicopter crashed through the roof of the Clutha Vaults pub.
Ten people lost their lives.
🔍 So What Caused This Accident?
The engines didn’t “fail”, they were starved of fuel.
“But there was still fuel onboard.”
Yea – that’s where things get interesting, especially for those of us who have never flown an EC135.
The EC135 stores most of its fuel in a main tank, but the engines don’t feed directly from it.
Instead, two electric transfer pumps move fuel into a much smaller supply tanks.
The engines draw their fuel from there.
As long as the transfer pumps are operating, everything works fine.
But…
If they aren’t, the engines continue running only until the supply tank is empty.
Which means:
The fuel that’s sitting in the main tank becomes inaccessible.
Something that requires careful consideration and management from a pilot’s perspective.
Investigators discovered that both transfer pumps had been switched off for an extended period.
As a result, the supply tank gradually emptied while approximately 76 kg of usable fuel remained trapped in the main tank.
Eventually, the LOW FUEL 1 and 2 warnings appeared.
They were accompanied by audio alerts specifically designed to grab the crew’s attention.
The warnings were acknowledged five times, but both warnings remained on continuously.
The right engine flamed out first, 32 seconds later, the left one too.
One of the most frustrating parts of this accident is that investigators could never explain why.
Why were both transfer pumps switched off?
Why didn’t the pilot decide to land at a suitable site?
Why wasn’t a MAYDAY transmitted?
The helicopter wasn’t fitted with a cockpit voice recorder or flight data recorder, so investigators had to piece together events using radar data, system memory and CCTV footage.
They could explain how the accident happened.
But some of the most important why questions remain unanswered.
One of those rare instances where asking “why?” can become a little frustrating!
The investigation team concluded:
“Incorrect management of the fuel system allows useable fuel to remain in the main tank while the contents in the supply tank become depleted.”
And:
“The RADALT and steerable landing light were unpowered after the second engine flamed out, leading to a loss of height information and reduced visual cues.”
Finally:
“Both engines flamed out when the helicopter was flying over a built-up area.”
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💡 What Can We Learn From This?
While it’s hard to determine lessons if the core question of “why” couldn’t be answered in the report, we can still learn quite a bit from this.
For me, the biggest lesson isn’t really about the lack of fuel, there are a few other things that are much more valuable.
Let’s take a look at the biggest take-aways.
Warnings are there to trigger human decisions
The low fuel warnings displayed were acknowledged multiple times.
And then remained on for the rest of the flight.
The helicopter did exactly what it was designed to do.
🔸 It detected the problem.
🔸 It generated multiple warnings.
🔸 It told the crew something wasn’t right.
A warning (on its own) doesn’t prevent an accident.
It only matters if it gets us to change what happens next.
The checklist states to land within 10 minutes. The investigation team did not find out why that did not happen.
Understanding your aircraft will eventually help you out of bad situations
We all know how much fuel we have on board, and how far it’ll get us.
But not everyone fully understands how that fuel actually reaches the engines.
This accident wasn’t caused by a lack of fuel, but by a lack of usable fuel.
That’s quite a difference, especially in the EC135.
Try to zoom in and understand:
🔸 different fuel failure situations
🔸 how does your fuel reach the engine?
🔸 what each warning actually means
🔸 how to deal with it
Sometimes, following a flowchart might not be enough to achieve a safe outcome.
When things get tough: Aviate – Navigate – Communicate
It’s easy to become fixated on diagnosing the problem. But the priority order remains the same:
🔸 Aviate: Fly the aircraft first. Maintain control, preserve rotor RPM if power is lost, and keep the aircraft in a safe flight profile. Memory items or immediate actions can be part of this depending on the situation.
🔸 Navigate: Decide where you’re going. If the checklist says to land as soon as possible or within a specified time, commit to that plan early.
🔸 Communicate: Tell ATC and others what you need, but only once the aircraft is under control and your plan is clear.
This accident is a strong reminder that nothing is more important than flying the aircraft and dealing with immediate issues.
That includes the “mission”. We’ve covered decision making when pressure builds here:
💭 Conclusion
Unfortunately, we’ll likely never truly know why the pilot didn’t land earlier.
But despite that, the Glasgow helicopter crash is one of those accidents that changes the way you think about knowing the systems in your own aircraft type.
Not just how to fly it, but how its systems actually work.
The most dangerous failures aren’t always the obvious ones.
They can be the ones hiding inside systems we think we already understand.
Pick up that training manual the next time you get some time to study, your life could depend on it.
You find the investigation report here.
Ready to learn from real aviation decisions, mistakes and challenges? Get our latest Notes from the Cockpit sent straight to your inbox, twice a month ⤵️
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