I would hazard a guess and say that most of Loganair's 145s are "hand me downs" from BA» when BA pulled out of a lot of UK▸ domestic routes, many of which were actually operated by Loganair in BA livery.
I looked at a sample, all of which were previously registered to BMI Regional, some from new in 2001.
The Q400 is capable of flight at higher levels, but my understanding is that the FL250 restriction is in place by regulatory authorities as it doesn't have drop-down oxygen for passengers (if the pressurisation goes at FL250, you have less airspace to dive through to get to levels where oxygen is sufficient than if you were higher).
The service ceiling for a Q400 is 27,000 feet*. There is a crew oxygen system supplied by a bottle in the nose, and three masks with microphone. The cabin crew have access to a portable oxygen bottle that can also be used for emergency supply to passengers, but you're right, there are no oxygen masks fitted above the passenger seats. The plan is for a descent to 14,000 feet to be made within 4 minutes, which is breathable. Decompression at 27,000 feet would probably not cause loss of consciousness on its own, although I don't think it would be at all enjoyable. The difference in pressure from 25,000 to 14,000 feet would be about 330 hPa on a rule-of-thumb calculation. The crew supply lasts at least 2 hours. In a nutshell, if a Q400 decompressed at its ceiling, and nothing else went wrong, everybody would survive, but they would be inconvenienced. The lack of passenger oxygen systems gives a reduction in weight and cost, and is actually a safety benefit. The ones that drop down in emergencies (or system failure more often) are fed from a chemical reaction, and cost several hundred pounds each. The reaction is exothermic, and fires have happened when they have malfunctioned.
Aircraft leasing is a very mysterious business, even more mysterious than train leasing. There are many leasing companies, many of them subsidiaries of the manufacturers, but the people who actually run the whole show are generally very anonymous, and sit at a level in the commercial world way above Richard Branson, Bill Gates, Donald Trump et al. They do very well out of the business, which has long been a source of puzzlement. Billions of dollars worth of serviceable aircraft are parked in deserts, the assets cost typically $250 million each and the airlines upgrade regularly, but even with a seat costing a pittance, a profit is turned at each level, except Flybe.
*The difference between 27,000 feet and FL (Flight Level) 270, if you were wondering, is the pressure. If you weren't wondering, skip to the next post. Up to a transition altitude, usually about 3000 to 5000 feet depending on the aerodrome, pilots set the altimeter to the "QNH" pressure, which is whatever a barometer at sea level would show for that area. They might land with "QFE" set, where the altimeter shows zero on the ground at the arrival airport rather than height above sea level. Above that transition altitude, the altimeter is set to the standard sea-level pressure of 1013.25 hectoPascals (hPa). This way, everybody flies at the same 27,000 feet, no matter what the air pressure is where they took off from. We recently had a pressure of 1050 hPa recorded in UK, and a low of 926 hPa has been recorded. That difference of 124 hPa represents an altitude difference of over 4,000 feet. Separation is usually 1,000 feet using the semi-circular rule: aircraft flying a course between 000° and 179° magnetic do so at flight levels with odd numbers of tens, those heading 180° to 359° on evens. Not having a standard altimeter pressure setting would lead to "loss of separation" in aviation jargon, or "collision" is common parlance. Next time you go to Mallorca, you will know why you go there at 37,000 feet , but home at 36,000.
To convert hectoPascals to millibars, multiply by 1.
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