I'm GMing a campaign today that will involve a combat between 6 T-47s (which have no weapons according to the CRB), and I want players to ram into each other. How would you determine damage and resolve attack rolls for a airship collision?

I would certainly use opposed piloting rolls for the attack and damage, but I like Seiito's suggestion to include stats about the vehicle as well. I'd probably utilize speed & size according to gunnery rules. For adjudication I'd likely take any successes and apply them to hull trauma, and any advantages would likely cause system strain unless we can come up with something better. On a triumph, the heroes will score a direct hit that disables the enemy vehicle and not theirs, and the opposite with a Despair.

Collision rules are on page 242 of the CRB.

Basically collisions cause a critical hit, subtract defence times 10 or 5 (depending on if its a minor or major collision respectively) from the critical roll. Apply strain (or wound?) damage to pilot/passengers as you deem appropriate, I'm pretty sure there's something on collisiongs/criticals causing strain to pilots/passenger in the CRB, but I cannot find it just now.

I believe a dev on the Order66 podcast mentioned the use of collision rules. I would rule it as a minor collision for the rammer, and a major collision for the target ship. Perhaps mitigate the rammer's collision if the ship is specially equipped with a ramming device.

I'd prefer something new for collisions than what is presented in the CRB. A head on collision that doesn't do any actual "damage" to the ship? That doesn't make sense to me. I'll be checking this thread for some ideas on how to handle damage for collisions in my games.

I have been testing a crunchier resolution for intentional ramming with my group. Here is the text from our test rules document (note that I intended to reduce the wall of text into an easy table once we finalised an iteration to make permanent in our game):

Pilot Action: Ramming
Silhouette: Any
Speed: special

In order to make a ramming attempt with any chance of success, the vehicle attempting to initiate the collision must be in Close Range with the target and be moving at a Current Speed equal to or greater than the target vehicle. The pilot make a Piloting skill check using the appropriate skill opposed by the Piloting skill pool of the target vehicle's pilot. For every point of Current Speed greater than the target, the ramming pilot adds 1 Boost die to their Piloting check to ram. The Handling ratings of both ships also modify the check accordingly as they normally apply to Piloting checks. The Defense Rating of the target ship also applies.

If successful, then the ships impact using the Collision rules on page 242 of the core rulebook. If the ships are the same or only 1 Silhouette different then the collision counts as a Major Collision for both. If the Silhouettes differ by 2 then it counts as a Major Collision for the smaller vehicle and a Minor Collision for the larger vehicle. If the Silhouettes differ by 3 or more then it counts as a Major Collision for the smaller vehicle and not at all for the larger vehicle.

Further, on a successful collision both vehicles suffer Hull Trauma equal to the Silhouette of the ramming vehicle times its Current Speed at the time of the collision. If the Silhouettes differ, then the larger vehicle suffers less damage (reduce effective Current Speed of the ramming vehicle by 1 for each point of Silhouette difference before multiplying for damage). This damage is modified by Armor. Advantage reduces the damage taken by the ramming vehicle by 1 each while Threat reduces the damage taken by the target by 1 each.

If the ramming vehicle is of smaller Silhouette than the target, it's Current Speed is reduced to 0 after a successful impact.
If the ramming vehicle is of equal Silhouette then both vehicles reduce their Current Speed by half their Silhouette (round up) after collision.
If the ramming vehicle is of greater Silhouette, then the target's Current Speed is reduced to 0 after collision while the ramming vehicle's speed is reduced by 1 unless the target is 2 or more Silhouette smaller.

Example #1: A desperate Rebel Alliance pilot in a Z-95 fighter decides to try and ram the enemy DP20 Gunship in an act of desperation. The pilot's Agility is 3 and Piloting(Space) is 2. His Z-95 is Silhouette 3, has a Handling of +1 and is moving at a Current Speed of 4. The enemy capital ship is Silhouette 5, has a Handling of -1 and is moving at a Current Speed of 2. The helmsman of the DP20 has Agility 3 and Piloting(Space) 2 as well.

The dice pool for this ramming attempt is 1 Ability, 2 Proficiency, 4 Boost (2 from having greater Current Speed by 2 points, 1 from +1 Handling of his own ship and 1 from the -1 Handling of the target ship), 1 Difficulty, 2 Challenge, 2 Setback (for the DP20's Defense Rating).

If the roll is successful, then the Z-95 suffers a Major Collision and the DP20 will suffer a Minor Collision. The Z-95 will also suffer 12 Hull Trauma (Silhouette 3 times Current Speed 4) reduced by 1 for each Advantage rolled on the check and by 3 for the Z-95's Armor. The DP20 will suffer 6 Hull Trauma (Silhouette 3 times Modified Speed 2 for the Silhouette difference) reduced by 1 for each Threat rolled on the check and by the DP20's Armor of 5.

Further, if it survives the Z-95 will end with a Current Speed of 0.

Example #2: Facing certain death, the crew of a GR-75 decide to try and ram the attacking Marauder corvette. The co-pilot assists in this daring act and provides a Boost die to the attempt. The GR-75 has Silhouette 5, Handling -3 and Current Speed of 3. The Marauder has Silhouette 5, Handling 0 and Current Speed of 2. Both crews have a Characteristic of 3 and Skill Rank 2.

The dice pool for this ramming attempt is 1 Ability, 2 Proficiency, 2 Boost (1 from co-pilot's assist action, 1 from having greater Current Speed by 1), 1 Difficulty, 2 Challenge, 5 Setback (3 from GR-75's -3 Handling, 2 from Marauder's Defense Rating).

If successful, then both ships suffer a Major Collision effect. The GR-75 will suffer 15 Hull Trauma (Silhouette 5 times Current Speed 3) reduced by Advantages and Armor of 3. The targeted Marauder will take 15 Hull Trauma reduced by Threats and Armor of 5.

Afterwards, the GR-75 will have a Current Speed of 0 (3 minus 3) and the Marauder will have a Current Speed of 0 (2 minus 3).

I'd prefer something new for collisions than what is presented in the CRB. A head on collision that doesn't do any actual "damage" to the ship? That doesn't make sense to me. I'll be checking this thread for some ideas on how to handle damage for collisions in my games.

A critical hit is damage to the vehicle, not hull trauma sure, but it's a lot worse in the long run as critical hits stack, severity will eventually increase, combat will become a lot more dangerous as systems shut down and one lucky shot can completely destroy your vehicle, as opposed to the crippled effect the vehicle suffers from when exceeding the hull trauma threshold (see the vehicle chapter on that). In fact a critical hit is somewhat more in the "make sense" department, as it's system specific, affecting specific parts of the ship and also affecting the overall structural integrity - those cumulative +10s to critical rolls ain't just for being mean. So, sure the ship can withstand laser attacks and suffer superficial damage as before, but one of those hits being nasty, i.e. activating a critical hit, it's going to get bonuses from your previous collisions, as the ship is weaker and closer to death.

Also, remember that minions can easily be destroyed by a critical hit, as per the standard minion rules, applying this for vehicle combat isn't outside the scope of the game or rules, if you so choose.

I understand that, but if I were to have a "major collision" in my car, it's not like just the steering goes out or I pop a tire, it's gonna be some damage to the body, or "hull". The faster I'm going, the more sever that damage is going to be.

Sure, but now you're applying real world physics to an adventure game set in a galaxy where there is sound in space, supernatural glowstick wielding monks, energy weapons of incredible slowness, heroes rarely if ever get injured and so on... the heroes are just that, heroes, they're supposed to withstand more punishment and it's only natural that this extends to their vehicles - and starship combat is dangerous enough as it is for an adventuring party, you don't need many hits on a light freighter to cripple it, and from thereon it isn't long until destruction if the enemy is determined to eliminate you.

Also, if you look to popular culture and sci-fi/space opera films, tv series, books and comics, they're often not all too realistic as it beats the purpose and goes against the premisses of a space opera/sci-fi universe filled with heroes that do cinematic, heroic and epic stuff. Collisions are not usually a big thing - or if they are it's plot vital (and this is the core of this whole game as I understand it, stuff important to the plot - both campaign and the immediate session - should pose a higher risk than random encounters and stuff like that.

Of course, if you want more realism - which is a fair position to take - then causing hull trauma would be a natural way to go, but keep in mind that this will make it all that much more deadly and space navigation all that much more dangerous in the short term. Unless you keep damage low... I mean, if the collision is a potential or predetermined outcome of the encounter, then one should definitely make more out of it, if not the I see no need for it.