Vaneev
There is a limit to roughness, although as Rainboe said, runways (should be) checked for performance and roughness and if the runway is operational you may assume it is considered acceptable. However ICAO guidance is very weak on the issue and the reality is that some runways can be rough (or can have 1 or 2 big bumps in them that really jolt the aircraft). Some ex-military concrete runways (especially in the Third World) can be real bone-shakers.
NASA found that the response of aircraft to runways required tentative limits on the vertical acceleration at the cockpit location. In practice, a runway could be judged as rough by some pilots and satisfactory by others. It was therefore necessary to relate roughness to cockpit acceleration, and concentrate repair efforts on those sections of the runway producing undesirable acceleration responses. Based on the NASA investigations,
an acceptable maximum incremental cockpit acceleration from a pilot’s viewpoint was established at +/- 0.4 g. This was considered to be the dividing line between satisfactory and unsatisfactory runways, and any greater acceleration could cause loss of precise control of the aircraft and subsequent pilot difficulties.
It was then observed at Anchorage International Airport that a runway which had been satisfactory for piston aircraft could cause undesirable cockpit accelerations in jet transports. Furthermore, not all aircraft are affected similarly by a given roughness pattern. That is, for a given velocity over a given runway roughness pattern, aircraft of different sizes will respond in different ways. This response is dependent on the natural frequency of the aircraft rigid body (and its size) and the elastic response, such that resonant patterns can be created between the aircraft and the runway unevenness pattern. Some good work was then done by Spangler and Gerardi (who I seem to remember was an ex-Lockheed landing gear designer) and they developed software to measure the runway profile and then calculate the dynamic response in the cockpit for the various aircraft during takeoff or taxi. It is complex stuff.
Boeing got involved in runway roughness, initiated by a request in 1968 by Ethiopian Airlines to comment on the condition of the runway at Addis Ababa, which was a representative example of a runway subjectively felt to be too rough by experienced pilots. According to the pilot reports, in a typical operation certain isolated bumps on the runway felt extremely hard during takeoff and landing, and the airplane resounded with sharp jolts that seemed much more severe than a hard landing. It was determined that the severity of the jolt varied with speed and the wavelength of the bump, leading Boeing investigators to believe that an objective criteria should be developed based on single bump height and spacing limits.
To cut a long story short, they came up with the Boeing bump criteria. This is based on a considerable amount of testing and analysis, and is a lot more sophisticated than it looks. It is easy to use, and needs only a local surveyor to take simple measurements. The FAA like it, and are giving serious consideration to adopting it as their new standard. Given that ICAO guidance is weak in this specific area, I reckon Boeing have done a great job here, and I have found it to work well in practice.
Here is the bump criteria that Sir George referred to:
