home *** CD-ROM | disk | FTP | other *** search
- Path: cliffy.lfwc.lockheed.com!news
- From: Ken Garlington <GarlingtonKE@lfwc.lockheed.com>
- Newsgroups: comp.lang.ada,comp.lang.c,comp.lang.c++
- Subject: Re: C/C++ knocks the crap out of Ada
- Date: Tue, 20 Feb 1996 09:23:02 +0000
- Organization: Lockheed Martin Tactical Aircraft Systems
- Message-ID: <312992F6.588D@lfwc.lockheed.com>
- References: <4etcmm$lpd@nova.dimensional.com>
- <4f4ptt$a1c@newsbf02.news.aol.com> <4g1b7n$l5@mailhub.scitec.com.au>
- <JSA.96Feb16135027@organon.com> <DMwFqr.EGD@thomsoft.com> <JSA.96Feb19193423@organon.com>
- NNTP-Posting-Host: ub_998356_mtm7.lfwc.lockheed.com
- Mime-Version: 1.0
- Content-Type: text/plain; charset=us-ascii
- Content-Transfer-Encoding: 7bit
- X-Mailer: Mozilla 2.0 (Macintosh; I; 68K)
-
- Jon S Anthony wrote:
- >
- > So, does this mean that there are _no_ confirmed cases of probes lost due
- > software? If so, I'm impressed as software has just plain _got_ to be
- > the weakest link in the chain. 1/2 :-)
-
- Actually, I would say that system requirements are the weak link in the chain,
- although the errors often tend to occur in software these days since more
- requirements (and particularly the harder, more volatile requirements) tend to
- be put in software.
-
- Three cases near and dear to my heart:
-
- For years, I have heard the story about how a "bug" in the F-16 flight control
- computer caused it to roll to an inverted position when crossing the equator. I
- have never found anything authoritative that exactly described the circumstances
- (if anyone has this information, let me know); but there are two points to be
- made about this:
-
- 1. Until relatively recently, the F-16 flight control computer didn't have any
- software in it. It was an analog computer.
-
- 2. Some people believe they heard this story in terms of the behavior of a
- handling qualities _simulation_ of the flight control system, in which
- the environment model only contained a part of the northern hemisphere. Someone
- decided to see what happened when you "flew off the edge of the earth."
-
- The other two cases are more recent and involve pilot-induced oscillations leading
- to an aircraft crash. In both cases, the press widely reported (in at least one
- case, quoting a senior executive at one company) that "the software got confused."
- However, the error in both cases was due to an interaction of the control law model,
- which can be implemented in either hardware or software, and the pilot. (The pilot
- will probably say the control laws were wrong; the control law people will probably
- say that the pilot operated the system outside its' limits. Both are probably right
- :). Nonetheless, because the behavior occured in software, that's what gets the
- blame.
-
- Dr. Levison's "Safeware" defines far issue much better than I just did, BTW.
-