Introduction / Context:
Runway longitudinal design must control gradient magnitudes and the rate of change of gradient for safe operations and pilot comfort. This question examines typical ICAO-aligned limits and the meaning of the rule on change of grade per unit length.
Given Data / Assumptions:
- ICAO recommends maximum longitudinal gradient around 1.5% for many runways (class and code dependent).
- A typical design control is a limit on the algebraic rate of change of grade expressed per specified length (e.g., 0.3% per 30 m).
- The first statement cites an unusual “distance between PI of extreme tangents to transition curve > 7500 m × sum of grade changes” which does not represent a standard ICAO formula.
Concept / Approach:
Vertical curve design often uses a rate-of-change constraint rather than arbitrary long distances. ICAO provisions cap gradient and rate of change to preserve sight distance and comfort.
Step-by-Step Solution:
1) Statement 1 reads like a nonstandard, dimensionally odd rule of thumb. It is not a recognized ICAO requirement; hence it is incorrect.2) Statement 2 (limit 0.3% per 30 m) is a standard-type control on rate of change of gradient—accepted as correct.3) Statement 3 (maximum longitudinal gradient 1.5%) aligns with ICAO guidance for many runways—accepted as correct.
Verification / Alternative check:
Check ICAO Aerodrome Design Manuals and Annex 14: you will find limits on max gradient and rate of change rather than the peculiar relationship in Statement 1.
Why Other Options Are Wrong:
Options including Statement 1 as correct are invalid because the stated relationship is not an ICAO formula.Single-statement options ignore the combined correctness of Statements 2 and 3.
Common Pitfalls:
Accepting arbitrary formulas without dimensional/standards check; confusing total grade change with the rate-control parameter.
Final Answer:
Only statements 2 and 3 are correct.
Discussion & Comments