I have flight logs for a WW II B-24 navigator who flew with a combat crew in China Burma India. There is a column for number of landings. The entries range from 1 to 5 or 6, mostly 1 or 2. The time can be as long as 8:00 to 10:00 or more. Why is the number of landings recorded? Is that still done today?
Yes, it's still done today, at least in military aviation.
It's to ensure that the undercarriage does not excede the number of landings it has to endure before being checked/overhauled/replaced. Landing an aircraft can typically be the most stressful regime of flight in terms of loading of certain bits of the aircraft, so it is pertinent to log how many times it happens per flight.
I'm not sure if this is specifically a military question or a general question. In general aviation (FAA) you are required to do a certain number of landings every 3 months to stay current. So landings are logged for this reason.
The specific regulation is 14 CFR 61.57 (a) (1), which says (emphasis added):
[…] no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days […]
I am not yet rated for IFR, so I'm not sure on the specifics about IFR currency mentioned in this regulation. The currency for VFR related flight differs from day and night; however, 3 night landings in 90 days will count to keep you current, while 3 day landings will only keep you current for daytime VFR.
A note on military training:
I was able to find this book/article that alludes to the training of navigators during the second world war; on P.585:
Before 1933 instruction in navigation was given only as part of pilot training.
If the individual in question had a military career and joined before '33 he may have been a pilot first and simply continued with the same log book. Why the landings were logged may just be force of habit. Either way its an interesting read on how difficult it was to be a navigator at the time and exactly what it took to become one.
Landing is not the easiest thing on an airframe! It imparts a lot of stress, and everything we build is designed and evaluated by some statistician to endure a certain number of uses + or - some standard deviation that he/she defines. Even the keys on your keyboard are meant to endure a certain number of presses.
Additionally, if you CAN collect data that you suspect may be useful later, why not? You never know when you may want to use it for something you didn't intend to.
Not sure about the navigator though.
For aircrew, yes there are certain requirements including no. of LDGs to be conducted within xx timeframe (typically 3 months / 90 days) in order to maintain currency. This information is recorded in the Pilot Logbook. Mine didn't have a special column (NZCAA type) so you would just write what was pertinent in the narrative, using as many lines as required.
For part 91 & 135 GA aircraft I'm not aware of any that require records to be kept of LDGs. In the airline industry cycles are recorded - this pertains more to the number of pressurisations, but on some a/c I believe LDGs are recorded also.
On the McDonnel-Douglas A-4K Skyhawks (Scooter in USN) that I maintained in the '80s we recorded LDG cycles, as well as g-force excursions. This pertains to airframe fatigue and cycle life. During peacetime fighters often last many more years (decades?) than would be reasonable for designers to estimate under true combat conditions, hence airframes can actually wear out, by reaching design time/life limits. This is especially applicable to naval aircraft operating from carriers. Even when the RNZAF operated A-4s, land based only, the initial "thump" of LDG usually produced more g, albeit momentarily, than a maximum performance ACM manoeuvre. They could have been landed "softly"; main RWY at their home field was ~2500m, but what the heck these were carrier aeroplanes and the pilots knew it. So they took delight in extending that 500mm or so of impact absorbing oil-damped undercarriage travel (top MX bikes have only 300mm) to its full effect. That was a good reason to log landings. JSB
All the answers to date seem to have missed the most obvious part: landing the plane is by far the most difficult (and arguably the most important) part of flying, at least VFR. So the reason a certain number of landings within a given period is required to maintain currency is simply to ensure that the pilot remains practiced in doing them. And the reason they're logged (and logbooks have a column for it) is so that you can show currency if you ever need to.
While landings might need to be recorded for some military or commercial airframes, it's simply not true for most aircraft.