During Hainan Airlines B737NG B-55*0 aircraft pilot training flight at ZSDY airport on April 16th, the aircraft triggered DON’T SINK EGPWS audio alert.
Honeywell engineering team has completed the data analysis and below is the analysis result.
MOD 3 EGPWS alert triggered at position Lat/Long: 37.55732/118.74794, EGPWC FH data can record 20 Sec data before EGPWS alert. Below data is the Rad ALT and ALT Rate for 20 secs before alert triggered.
The ALT Rate is already changed to negative value, and the Rad ALT loss from 1387 to 1261, the alert triggered at RAD ALT 1261 ft. When the alert triggered, the landing gear is in down position and the FLAP is around 15 degree.
| Rad Alt | Alt Rte | Gr Dn | FlpAng |
| 1387 | -741 | 1 | 14.8 |
| 1381.3 | -529 | 1 | 14.8 |
| 1397.3 | -335 | 1 | 14.8 |
| 1390 | -207 | 1 | 14.8 |
| 1364.8 | -5 | 1 | 14.8 |
| 1364.8 | 26 | 1 | 14.8 |
| 1359.5 | 20 | 1 | 14.8 |
| 1358.5 | -48 | 1 | 14.8 |
| 1364.5 | -163 | 1 | 14.8 |
| 1362 | -274 | 1 | 14.8 |
| 1363.5 | -352 | 1 | 14.8 |
| 1362 | -439 | 1 | 14.8 |
| 1349.8 | -569 | 1 | 14.8 |
| 1343.5 | -650 | 1 | 14.8 |
| 1328.3 | -700 | 1 | 14.8 |
| 1315.8 | -711 | 1 | 14.8 |
| 1303 | -665 | 1 | 14.8 |
| 1295.8 | -678 | 1 | 14.8 |
| 1282.3 | -733 | 1 | 14.8 |
| 1261 | -835 | 1 | 14.8 |
Below is the flight path figure before the alert triggered.
The MODE 3 triggered because the aircraft status conform MODE 3 logic and altitude loss already penetrate MODE 3 Envelope at RAD ALT 1261 FT. So this is a correct true EGPWS alert.
这个图是这样看，横轴是无线电高度，纵轴是掉的高度。掉高度是从高度率开始变负值计入初始值。以后的高度比这个高度低的差值就是altitude loss。也就是1387-1261=126，高于的该值。由于计算机只能记录触发前20秒的值，实际可能比这个更高。
这个触发应该还是计算机以为飞机是在起飞阶段，而不是降落阶段，因为机组是飞训练操作导致的，机组想降落，但是计算机认为你是在起飞，所以产生了这个警告逻辑