The argument concerns which statistic is more reliable. The impact of building runways closer together on pilots’ level of caution doesn’t bear on which statistic is more reliable.

The flight reports are “required of pilots”; this indicates the pilots are the sources of the reports. (B) points out that this information can be unreliable, because pilots who stray off course — which is a mistake — might not report that mistake.

The argument doesn’t question the integrity of any individuals. It relies on premises concerning the basis of the two statistics. Neither of these statistics comes from those who are against closer runways.

The author doesn’t assert that the tapes cannot provide accurate information. The author’s complaint is that the review of those tapes is only “partial.” So the author is open to the possibility that information in the tapes is accurate; it may be accurate, but incomplete.

The author doesn’t conclude that the 1/20,000 figure is inaccurate, only that it’s less reliable. Also, the basis of the conclusion is not a lack of conclusive evidence for the 1/20,000 figure. The basis is a comparison of the sources of the two figures.