UFO Crash Recovery

Overview

Exercise caution - There may be operatives in the UFO or around the crash site. Your mission will be successful when all enemy units have been eliminated or neutralised. Recovery of UFO remains, artefacts, and alien corpses can then be initiated.

Specific listings of items that can be recovered from each UFO type can be found by following links on the UFOs page. However, those listings do not (yet) reflect the effects of a crash landing on recoverable items, particularly the all-important Elerium and Power Sources. For this, see the next section.

Power Source Explosions and Elerium Recovery

When UFOs crash land (except the Small Scout, which has no engine), there is a 75% chance that its Power Source(s) will explode, which also destroys their Elerium. It is an extremely powerful explosion, usually even stronger than a Blaster Bomb. Power Sources (PSs) explode with an average (rated) strength of 215 ± 35 HE (min 180, max 250(!!)). The actual equation used is 180+(Rnd#×70). A PS explosion is always enough to destroy any Elerium caught in its blast, and its blasts have a radius of 11 tiles (diameter 23), as wide as a Blaster. It is thus a great mystery how the Medium Scout has any survivors after the power source blows.

In terms of Elerium recovery, all but the Supply Ship fall into two easy categories:

Isolated PSs

In four UFOs, the PSs can never impact other PSs. 25% of the time, you'll recover 50 Elerium from each PS. In other words, you get an average of 12.5 Elerium per PS, and it's additive:

Medium Scout, Large Scout, 1 PS: Average of 12.5 Elerium

Abductor, 2 PSs: Average of 25 Elerium

Battleship, 4 PSs: Average of 50 Elerium

On average, 1 PS is left on a Battleship (25% x 4 PSs). Only 0.39% of the time will all 4 PSs be intact (0.25⁴).

Adjacent PSs

If one blows, all Elerium is destroyed. So the chance that any Elerium is left, is the chance that not a single one blows - it's 0.25 raised to the number of PSs.

Harvester, 2 PSs: Average of 6.25 Elerium (6.25% chance of 100 Elerium)

Terror Ship, 4 PSs: Average of 0.78 Elerium (0.39% chance of 200 Elerium)

This is why the guts of a crashed Terror Ship are almost always a smoking crater... only once every 256 crashes (0.39%) is there not an explosion with the strength of a Blaster bomb (or worse)!

Supply Ship

This one is an oddball, because if a side PS explodes it takes out the middle one (before it has a chance to explode), but just barely doesn't reach to the PS on the other side (the explosion radius is 11). Yet if the middle one explodes, it takes out all 3 PSs. So there are three possible scenarios with PSs left: only the left-most PS left, only the right-most PS left, or all 3 PSs left. But there are two ways to get to the right-most PS being left, and one of those ways has a higher chance of happening than the other.

The table below was first made by constructing a simple Yes/No table of the eight possible combinations for the 3 PSs blowing (Y) or not (N). Then I filled in by hand how many engines would be left. Then I constructed a simple odds table (75% chance if there was a Y for that PS, 25% if not), multiplied the three odds for a cumulative probability, and finally multiplied the cumulative probability by the number of engines left, times 50 for the Elerium PSs hold. As a last touch, I sorted on decreasing cumulative odds (i.e., probability):

  PS Explodes     PSs    Odds for PS ...      Cum.   E115
  L    M    R    Left     L     M     R      Odds    Left
  Y    Y    Y      0     0.75  0.75  0.75    .422    0.00
  Y    N    Y      0     0.75  0.25  0.75    .141    0.00
  Y    Y    N      R     0.75  0.75  0.25    .141    7.03   Note 1
  N    Y    Y      0     0.25  0.75  0.75    .141    0.00   Note 2
  N    Y    N      0     0.25  0.75  0.25    .047    0.00
  Y    N    N      R     0.75  0.25  0.25    .047    2.34
  N    N    Y      L     0.25  0.25  0.75    .047    2.34
  N    N    N     All    0.25  0.25  0.25    .016    2.34
                                   Totals   1.000   14.06

Notes:

• (1) If the left one blows, it kills the middle, even if it was "supposed to" blow, and the right PS remains, at a high-ish chance... but
• (2) if the left PS doesn't blow and the middle one does, they're all dead. Zero chance of any Elerium.

So. The total cumulative probability is 100% (check). And the final answer is: 14.06 Elerium is recovered from Supply Ships, on average. Here is what you'll tend to see:

 PS(s) Left    Likelihood
 None             74.9%
 Right-most       18.8% 
 Left-most         4.7%
 All three         1.6%
                 100.0%

Due to its layout, the Supply Ship is also unique in another way. In other ships with adjacent PSs, all the other PSs are destroyed if just one of them explodes. In other words, only one can actually explode. But in the Supply Ship, the two end PSs can explode, and it's possible to have the damage from these two huge explosions superimposed in the mid area between the two PSs. This has a 56.3% chance of happening, via "two" ways (the first two lines in the table). If both of the PSs blew with high strength, there will be extensive roof damage, letting you see into the floor above (and raw dirt beneath). The left PS damages the pristine roof/floor tile to its damaged (a.k.a. "dead") tile with HE from 80 to 125, but doesn't have the 130 needed (260/2; it can't be over 255) to completely vaporize both the pristine tile and the damaged tile... and then the right PS blows and easily adds the 50 HE needed to vaporize a number of damaged tiles in the middle. The damage would be much more extensive if the inner UFO walls didn't prevent the first blast from damaging a lot more tiles; there may not have been any floor left in the middle of the second level, to go from one end of the UFO to the other on that level.

For the record, PS explosions differ from other explosions in a couple of ways - although for all practical purposes, you'd never know the difference. For more info, see Explosions#UFO_Power_Sources.

Field Notes: Clearing a landing site with JFG

Here's one I was so proud of I took notes. This was about Dec 2003. Nothing really weird here, but just went really professionally, without losing anybody. May I present:

• Sectoid, large scout crash, farm in california, early evening, Superhuman difficulty.
• 8 soldiers and a rocket tank respond.

Loosely numbered turn-by-turn, actually event-by-event.

Events

0. Successfully deployed in circle around Skyranger with no sightings.
1. Tank scouts first. Alien sighting by tank. Squaddies do 2-stage alien grenade relay. Takes out a hidden alien and part of a wall as well as the target (2 kills)
2. Tank sights a second alien, fires rocket, misses. Squaddie takes armed grenade, approaches, then crouches behind tank before throwing. (Out of sight so no reaction fire.) (3rd kill)
3. Scout (with RE of 60) moves in a different direction, spots one and freezes. Support sniper with rifle takes the shot (FA of 64, 87% chance) and hits. (4th kill)
4. Tank sights a third among the stables and stops. Squaddies manage to land a grenade in the area. (5th kill)
5. Aliens' turn, tank is shot at and responds with rocket fire. (6th kill)
6. Scout found one, support sniper hits but does not get a kill. A tossed HE pack misses, and no-one is in range to add a grenade. End of turn. Alien does not kill scout; sniper is successful on next turn. (7th kill)
7. Tank flushes an alien but is blocking support fire. It moves to clear the line of fire and is slightly damaged by reaction fire by doing so. Support fire takes out the alien. (8th kill)
8. Team finishes sweep and gathers at UFO door for a breach. At the start of the breach turn, the tank fires a rocket into the diagonal walls forming the inside corner of the cross. This kills one alien (9th kill)
9. Craft is filled with smoke. Two additional corpses are seen. The second squaddie in has enough TU's to push forward into the hollowed out centre; he sees an alien at the bridge of the ship and freezes. Third, fourth, and fifth breachers take up kneeling positions inside the door and start shooting at the alien through the smoke cloud; the third shot drops it. (10th kill)

Score sheet

Alien kills registered - 9
Corpses - 9
Captured aliens - 1 (soldier rank)
Artifacts - 41
Alloys - 31
Nav consoles - 2
(Engines destroyed in crash)
Soldiers KIA/MIA - none!
Final score 275.