T-VASIS versus PAPI
Lewis (20111) compared the accuracy with which a group of ab-initio pilots tracked the correct approach-to-landing glide path when using two different approach lighting systems (T-VASIS4 and PAPI5). Results (see illustration 1) show that pilots were better at tracking the correct glide slope in 8 scenarios out of 10 when using T-VASIS and in 2 scenarios out of 10 when using PAPI. On average, ab-initio pilots performed better with T-VASIS (mean difference = 6), a sensible difference of moderate magnitude (see Perezgonzalez et al, 20132).
|Illustration 1. Average deviation from glide slope*|
|(* Angular deviation from 0, multiplied by 100)|
When questioned about their perception of fit-for-purpose and preference for one lighting system or the other, most pilots perceived T-VASIS as being a better visual system when flying on the glide slope or when above it, but perceived PAPI as being a better visual system when flying below the glide slope. Irrespective of perception, though, most preferred PAPI over T-VASIS.
|Illustration 2. Assessment of best-fit-for-purpose and preference for approach lighting system|
|Number (%) of pilots who think best displays when||Number (%) of pilots|
|On glide slope||Above glide slope||Below glide slope||Who prefer|
|PAPI||6 (42%)||3 (21%)||8 (57%)||9 (55%)|
|T-VASIS||8 (57%)||11 (79%)||6 (43%)||5 (35%)|
Generalization is limited, if at all possible, to ab-initio pilots with about 21 flying hours. The main limitation of the study is that the low experience with flying may account for the variability in tracking the flight path (with T-VASIS offering more precise feedback than PAPI, thus the better performance). The results seem of little relevance to any other population.
Jose D PEREZGONZALEZ (2013). Massey University, Turitea Campus, Private Bag 11-222, Palmerston North 4442, New Zealand. (JDPerezgonzalez).
Want to know more?
- LEWIS (2011) original article
- The original article provides full detail about the research.
- Skybrary - VASIS
- This Skybrary page offers a small introduction to different visual approach slope indicators (such as T-VASIS and PAPI).
- WikiofScience - Ab-initio pilots' performance using T-VASIS versus PAPI
- A detailed review of Lewis' article done by Perezgonzalez et al (2013).