OK, everyone here who codes in ADA, raise your hand. Atlas?
On projects like this I would worry more about accumulated technical debt from decades of modification than the language they're written in. (I suppose the language can complicate the task of hiring programmers who are skilled with its idiosyncrasies, but that's hardly an insurmountable or crippling problem.)
Our compiler package also came with an extensive concurrency API that offered a variety of threadsafe containers comparable (again) to java.concurrent - and this was software from the late 80s/early 90s!
What was bad about Ada was Ada 95. It strove to make Ada into an object-oriented language, but did a poor job of it with some very tortured syntax. edit what Masklinn said - "bolted on" is a perfect way to put it.
1. It's a very lawyery language, there are very few things the compiler will accept to infer, which makes Ada tedious to read and write.
2. The strange mix of underscores and uppercases that is the normal Ada writing style (I believe Ada identifiers are case-insensitive, code from the 80s tends to be VERY_UPPERCASE_HEAVY while the same code now Tends_To_Be_Strangely_Capitalized) makes my head hurt.
And since this is avionics, they're probably dealing with embedded code (which tends to be even less readable) as well...
And as totalc notes, the OO additions of Ada 95 (if you have access to them) feel very bolted on and unnatural.
Though I can't claim any professional experience, lots of my college education was straight from DoD/Navy expats who wrote military software.
There are lots of firms in the midwest that write this kind of software. John Deere, Lockheed, etc.
Most static typed languages - C, Java, Haskell, etc are memory representation centric in their primitive types. Ada is usage centric.
You see that two ways.
First, in most languages any item with underlying implementation X can represent any legal value of X, even if it makes no sense. If you want to represent a quantity whose maximum value is one million, putting it in anything shaped like a 32-bit int will let it contain the illegal value "one million and one". Contrast Ada which will let you cap its legal range.
Second, in most languages any item with underlying implementation X can contain anything else with the same implementation. Your typedef'd int can be put into anything else int-sized. Contrast Ada, which won't permit you to mix apples and oranges if they are defined as distinct types with int storage.
The Ada class started in '94 if a timeframe helps
Well not really, but Ada is alive and well in the guise of PL/SQL. You can see it if you look closely, type "desc sys.diana" into any Oracle DB, DIANA is "descriptive intermediate annotated notation for Ada".