Since @EliotHiggins and others asked the other day: How many of these Mi-8/17 helicopters, which have been responsible for so much suffering over the years, are actually still in action? Let me try and offer an estimate. As always, the answer has a lot of caveats. /1
First off, what are we talking about? The Mi-8/17 ("Hip") are relatively large, Soviet-designed transport helicopters. At the outset of the war, the Syrian air force had a relatively large fleet of these on the books (50+ airframes) in line with Soviet-influenced doctrine. /2 
Since 2012, these were employed for (1) VIP transport, (2) reconnaissance, (3) supply of remote government-held pockets, and - most notoriously - (4) as improvised bombers, indiscriminately dropping explosive-filled barrels onto opposition-held towns. /3
But you knew that! Let's do the count: Sattelite imagery is our first stop. Helicopters generally easy to spot because they are not moved into hangars but stand out in the open. The most recent count I'm aware of is @JanesINTEL from early 2018, which identified 53 airframes. /4
Based on open sources, Jane's also estimated that 40-50% of SyAAF airframes are routinely out of service. In a separate assessment later that year they put the number at roughly 15 active Mi-8/17 in service. But this tells us little about their serviceability or deployment. /5
I agree that's a realistic range. So once we subtract those airframes that have been obviously lost, those that have not moved in months or years and the 2-6 airframes usually in maintenance at the Aleppo/Nayrab servicing facility, we then move to discount on military purpose. /6
This is easiest for the comparatively small number of "special-purpose" Mi-17s (spioenkop.blogspot.com/2018/10/flying…) as well as those routinely deployed to remote eastern bases (principally Hasakeh and Deir Ezzor) on transport duties. We're looking for barrel bombers first and foremost. /7
Alright. We're getting closer. Now we're talking six to twelve airframe range which will be deployed close to front lines tracking with ongoing ground operations. This is where we start mixing methods: satellite imagery, open-source identification and flight pattern analysis. /8
I'm gonna cut this short, but once we near rebel-held enclaves we get access to tracking data collected via a complex network (wired.com/story/syria-ci…) of sensors and observers who work tirelessly to provide early warning to communities in the path of these flying war crimes. /9
We match sorties (incl from ad-hoc bases such as the "tank school" and Safira factories) to satellite and open-source imagery to track deployments throughout the war. Below, the Tiger Forces "barrel bomb" squadron shifting from Aleppo to Homs to Hama to Damascus (2016-2018). /10
Not relevant for airframe count, but we can match those flight patterns to impact. See below our chart on attacks in the Ghouta offensive (2018). In mid-February, the Tigers arrive from Hama to Dumayr and with them the barrel bombings. We can break this down sector-to-sector. /11
As we follow these guys around (and add other sources such as radio intercepts), we get ever better at connecting the micro to the macro picture. For example, we can identify the precise helicopter that dropped the Chlorine barrel bomb on Saraqib in February 2018 ("1253"). /12
But enough about attribution. The macro-data is useful for identifying the relevant subsets of helicopters associated with specific attack patterns (here conventional and chemical barrel bombs). We can also see daily and weekly sorties "ceilings" and helicopter availability. /13
Alors. Long story short, we estimate there are six to ten Mi-8/17 helicopters more or less consistently involved in the SAA or Tiger Forces barrel bombing campaign (incl. hundreds of Chlorine attacks) responsible for innumerable war crimes and thousands of civilian deaths. /14
These are usually deployed in small squadrons on small exposed forward operating bases, where a single well-placed salvo could have done devastating damage. The introduction of MANPADS is good but not enough as they merely raise the ceiling thus further reducing precision. /15
Finally, I am merely offering a glimpse into what we and international investigators know about these helicopters and associated Syrian formations. I can ramble endlessly about this. Way more will presumably be released over the years as accountability initiatives proceed. /16
A few gaps: In my estimate, the number of helos is small enough that they can each be individually "fingerprinted". This is tedious work which would help prosecution immensely. Second, we have some understanding of the community and political impact of barrel bombs, but... /17
In order to fully understand their deployment, it would be helpful to have proper CEPs for various munition configs. I have tried to do some of this digitally and mathematically but I think the only solid way is live testing. So lemme know if you have a helo and a range! /18
Apologies for the myriad of editing mistakes and leaps in logic. I threw this up quickly because the two shoot-downs this last week brought some insane nonsense back into my mentions. /PS
