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In the ongoing story about someone trying to rescue dogs from a volcano with a drone, I keep seeing variations of this claim repeated:

Spanish authorities have dropped food down to the dogs with drones, but no one has come up with a plan to save them until now. Helicopters aren’t permitted to fly into the area because hot gases emitted by the volcano can damage their rotors. And it’s clear that no one can go in on foot with the volcano still in a volatile state.

Something feels off about this. My non-expert brain sees a few options here:

  • Maybe there is ash in the air, and that may damage the rotors? (but the clarity of pictures like those on this article don't suggest a BA 009 scenario to me)
  • There's not enough oxygen available to support combustion or human life (but apparently enough to sustain dogs?)
  • The air is hot enough that its density can't support flight (but, again, not hot enough to kill dogs?)

None of these explanations make much sense to me. Does anyone have insight into what's really going on here?

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    $\begingroup$ Don't we think first that while it won't actually hurt the rotors themselves, "hot gas" might well harm the lift capacity, of the function of the engines, or both… and then that if "no one can go in on foot…", rather than "risk going in…" the dogs are already dead ducks? $\endgroup$
    – Robbie Goodwin
    Oct 22, 2021 at 0:03
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    $\begingroup$ "And it’s clear that no one can go in on foot with the volcano still in a volatile state." → Well, well, well... $\endgroup$
    – walen
    Oct 22, 2021 at 11:32
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    $\begingroup$ WRT ash, which is a different, though related issue: even if there is no ash in the air beforehand, there will be a lot thrown up by the downwash in landing a helicopter, or even hovering it and lowering someone (look at pictures of how helicopters kick up spray during sea rescues.) $\endgroup$
    – sdenham
    Oct 22, 2021 at 13:26
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    $\begingroup$ Seems more likely to me that they are worried about ash being ingested into the engines, and coating the turbine blades. Short editorial (in)correction from there to say rotor-blades. $\endgroup$
    – MikeB
    Oct 22, 2021 at 15:57
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    $\begingroup$ Rotors are sometimes made from composites such as carbon fiber oor glass in an EPOXY matrix. Epoxy. Not just metal. $\endgroup$
    – DKNguyen
    Oct 23, 2021 at 2:08

3 Answers 3

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the clarity of pictures like those on this article don't suggest a BA 009 scenario to me

But that situation can change during the rescue, i.e. a new eruption.

As for the claim:

Can volcanic eruptions endanger helicopters and other aircraft?

Yes. Encounters between aircraft and clouds of volcanic ash are a serious concern. Jet engines and other aircraft components are vulnerable to damage by fine, abrasive volcanic ash, which can drift in dangerous concentrations hundreds of miles downwind from an erupting volcano. [emphasis mine]

— usgs.gov

Note what it says about the abrasive ash, which can fail a helicopter's turbine engine. Heat is not discussed on that page, but it's not the first time the media oversimplified the situation, and also the linked article as of writing this does not quote its source. Nevertheless, a new eruption and/or the existing ash makes more sense. The Guardian also quotes the ash:

Reaching the animals on foot is impossible as this would require crossing scorching lava, and helicopters cannot fly in the area because the ash and hot gas from the volcano could damage their rotors, said Leales.org spokesperson Alejandro Molina. "This is the only way to do it," he told AFP.

— Drone rescue plan for dogs trapped by La Palma volcano. 20 Oct 2021. theguardian.com.

Also as the quotation above shows, the AFP article used by The Guardian is likely the origin of the claim that was truncated by gizmodo.com. Alejandro, the animal shelter spokesperson, most probably just relayed what the pilots said when this was considered.

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    $\begingroup$ To clarify this on this, while normally dust particles wouldn't be a problem to machines - most have a huge tolerance build in. Volcanic ash is kind of different, it is both very sharp, and the heat makes it (for the lack of a better word) "sticky" to metals, the combinations allows easy build up of ash in moving parts, stalling motors. $\endgroup$
    – paul23
    Oct 21, 2021 at 10:59
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    $\begingroup$ @paul23: Right, while helicopters fly commonly in sand clouds in desert areas (albeit this is not without consequences for the engine), silicates in volcanic ashes have a lower melting temperature, found in turbine (1000-1800°C). This was the reason for grounding aircraft during the Icelandic volcano episode. $\endgroup$
    – mins
    Oct 21, 2021 at 11:28
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    $\begingroup$ @mins or even more relevant: en.wikipedia.org/wiki/British_Airways_Flight_009 the eruption of Mount Galunggung which is a near accident and something you kind of want to prevent. $\endgroup$
    – paul23
    Oct 21, 2021 at 12:36
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    $\begingroup$ Let's not forget the Eyjafjallajökull eruption, which caused weeks of air travel disruptions over the Atlantic. $\endgroup$
    – Sebastian Lenartowicz
    Oct 21, 2021 at 14:04
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    $\begingroup$ Good news... The dogs were rescued yesterday by a group of daring dog lovers who reached them by foot, defying official restrictions... twitter.com/RTVCes/status/1451174077968883720 $\endgroup$
    – xxavier
    Oct 21, 2021 at 14:34
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Look up "Twilight Zone Accident" on Wikipedia. This occurred when a pyrotechnic charge went off in proximity to a helicopter's tail rotor, causing the composite blade of the tail rotor to disintegrate from heat. The helicopter then spun out of control, crashed, and killed three people.

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Flying is all about risk mitigation. Any time you start a helicopter you are taking a risk that some accident might happen. So you, as example, make sure that the area around the helicopter is free from debris that might be blown around and possibly harm the helicopter or anything else. Flyers spend a lot of time avoiding risks, for example by making sure there actually is fuel aboard for the planned activity plus a safety margin. (I always checked visually before start, not relying on possibly faulty meters).

The handbook of the helicopter describes known limitations, say as to air temperature and pressure height, maximum loading and so on. The aircraft has actually been tested up to this limit, albeit by experienced test pilots. But outside the limits you are on your own. Flying inside an active volcano is not tested nor described in the handbook, so the pilot is on his own there. To go or not to go, that is the question?

My belief is that the situation would have been different if it were people that was in a difficult situation. In this case the risk equation (person saved) / (helicopter accident) would be larger then if the gain would only be (dogs saved). Simple going over the dogs with a very noise helicopter might as well scare them off, while a person would assume that it was a rescue operation and cooperate.

So, in the end, the decision was to not fly the helicopter. Then you need to tell this decision to a general public that, generally, has no idea of what risk is. So you make up an "excuse" that it could damage the rotor blades. Well, it possibly could, as it could possibly damage just about anything else on the helicopter.

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    $\begingroup$ +1, good points, still we don't know if they decided not to fly the helicopter, maybe there was no hero to pilot it or no owner ready to sacrifice an aircraft, and the Air Force just declined the request. $\endgroup$
    – mins
    Oct 21, 2021 at 10:34
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    $\begingroup$ I think the pilots were unlikely to make up excuses. Probably there was a misunderstanding on the part of the spokesperson here. Turbine, compressor etc. easily translate to rotors on the head of a layperson. $\endgroup$
    – Jpe61
    Oct 21, 2021 at 16:29
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    $\begingroup$ @Jpe61 Agree. Most probably it was some spokesperson that gave the reason in order to tell the general public. $\endgroup$
    – ghellquist
    Oct 21, 2021 at 20:23

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