Incident report

 

Airspace intrusion during emergency

 

 

General information

 

Aircraft type                                               Pierre Robin 100/210

Aircraf reg                                                 SE-FNC

Flight                                                         Private

Date of occurrence                                     July 10, 2008

Operator                                                    Allan Emrén

From                                                         LFBI

To                                                             EHGG

Place of occurrence                                    EHWO

Time of occurrence                                    11.15 Z

Type of flight                        Non commercial

Persons on board                                       2

Flight phase                                                Cruise

Altitude                                                      690 - 1230 feet

IAS                                                           110 knots (fluctuating 90 - 130)

Met conditions                                           VMC - IMC

Crew workload level                                  Extremely high

Name of pilot                       EMREN

Phone                                                        +46 (0)708 118836

E-mail                                                        allan@nuchem.se

 

Pilot data

Total flight time                                           1435 hours

Flight time during last 90 days                     43 hours

Licence type                                              PPL

Valid until                                                  14/06/2010

Ratings                                                      SE Piston (land), Night qualification

Supplementary education                           IFR (no rating in this case)

 

Weather conditions

Visibility         < 5 km. Temporarily <1 km

Clouds:          Generally 1000 - 1200 feet, temporarily < 500 feet

Turbulence:    Moderate to severe

 

ATS Flight plan                                       LFBI - LHGG

 

Planned route across the area

CMB, NIK, point DELTA of EBAW, BC (as GPS coordinates 513000N 042230E), PAM

 

 


Subjective experiences during the incident

 

After take off from LFBI, the weather conditions were CAVOK until the Paris region. Not far from the BVS VOR, I was advised that rain showers were approaching from the west. This was a bit earler than predicted, but as I was heading towards north east, I deemed that being in the outer parts of the shower area, and heading partly away from them, they would not cause any real trouble.

 

The sky gradually became overcast with a cloud base that was generally 1500 - 2000 feet. Obviously, there were embedded CB's visible as dark areas in the overcast, and also occasionally as rain showers. In the showers, the cloud base went down to 1200 - 1500 feet. Only light turbulance occured. The visibility appeared to be about 5 km in the showers.

 

After passage through one shower, I was advised that the transponder mode C showed 5000 feet, although I was, as I remember it, at 1200 - 1500 feet. I was ordered to change to mode A. The probable cause was that water or humidity had caused a short circuit or a change in resistance of some resistor.

 

Some time later, I was advised that radar contact was lost. Quality of radio connection decreased from 5 to 3 with respect to receiving. During transmission, a lot of noise was heard.

 

I could see the reply lamp blink on the transponder unit, so obviously, I was seen, but had no idea about who was seeing me.

 

 

Shortly before reaching NIK, the aircraft was hit by severe turbulence making the control very difficult. At the same time there was a decrease in cloud base and visibility. It also started raining, which caused the windscreen to get blurred. While struggling to keep the aircraft under control and free of cloud, I was forced to let go of attention to position, and focus upon avoiding obstacles, that were numerous in the area. Among those, I could see a huge cooling tower, that I had to avoid overflying. To the right of the aircraft, stratus clouds were seen close to the ground.

 

To see through the wet windscreen, I had to release the shoulder parts of my seatbelt so I could lean forward having my eyes closer to the window. Otherwise, the eyes focused on water drops, rather than on the surroundings. In the poor visibility, towers were generally not visible until they were a few hundred meters away (IMC conditions). When the conditions eventually grew better, I had no idea about my position. Trying to follow my path on the map while keeping the aircraft under control, evading obstacles and  keeping free of clouds was out of question. This would not have been survivable.

 

The deviations were large enough, to make the path line disappear outside the display of the GPS. With the VOR, I was able to find an approximate direction towards PAM, and turned as close to that as the weather permitted. When the flight was stabilized, I could change scale of the GPS to start approaching my intended path.

 

By then, it was obvious that the weather conditions were worse than told by the prognosis, so I started looking for alternatives to EHGG, as it looked doubtful that I would be able to reach my destination. The weather conditions got worse again with lowering cloud base and decreasing visibility, and I decided to turn 180 degrees back to my arrival track and ask for vectors to a suitable airport.

 

During approach to EHSE, the conditions again improved, and there, the cloud base was well over 1000 feet and the visibility more than 5 km. There was a light rain, but not enough to decrease visibility through the wind screen. So the landing there was uneventful. After landing, I learned that I had been close to EHWO.

 

 

Objective data on the incident

 

Flight path

 

In the section above, I have described my subjective experiences during the incident. From the GPS unit, I have been able to retrieve data on the interesting part of the flight. The data ranging from 11.01.04 Z to 11.23.14 Z are plotted in Figure 1.

 

Figure 1. Overview of the situation. Intended path is shown as green lines. The real path is the dark blue curve. Position of EHWO is marked by a red circle.

 

 

In the figure, it is clearly seen that the flight was conducted close to EHWO in accordance with the radar data. I reality, EHWO is not a point, but has an extension, why the distance might have been even smaller. It is also seen that the distance between the intended path and the real one differs by several miles most of the time, illustrating the problems caused by the weather conditions. A more detailed view is shown in Figure 2.

 

Figure 2. Detailed view of the most critical part of the flight showing several turns to avoid obstacles and clouds.

 

 

In Figure 2, dots are plotted along the track. Each dot represents a sampled position in the log file. Temporal distance between the dots is five seconds. The planned route is shown as green lines.

 

It is clearly seen that flying along a straght line was impossible due to clouds and obstacles. At the altitudes in question (800 - 1000 feet), even the smallest cloud could hide an obstacle. Therefore it was necessary to keep away from clouds at any cost.

 

 

Turbulence

 

As is well known, turbulence appears when the aircraft moves through regions of air with different directions of movement. The most common results from the point of view of the aircraft is rotations along its axis, variations in IAS, and vertical accelerations. Although all three kinds occured during the incident, there is no equipment on board to record the first two kinds. From the GPS record, however, rapid variations in altitude gives a record of the vertical turbulence. This is illustrated in Figure 3, covering the same time interval as Figure 1, e.g. 11.01.04 Z to 11.23.14 Z.

 

Figure 3. Vertical acceleration events caused bu turbulence.

 

 

A sloppy definition of severe turbulence is turbulence intense enough to make objects that are not secured to fly through the cabin. This happens when the vertical acceleration exceeds about one g (9.81 m/s2). As is seen from the figure, the turbulence encountered, has to be regarded as severe. This, also was the subjective experience during the flight, as mentioned above.

 

For the aircraft, Robin 100/210, the design load factors without flaps is 3.8 g for positive loads and -1.9 g for negative loads. If the design load factors are exceeded, the structural integrity of the aircraft is endangered. In Figure 3, it looks like the limit has been exceeded for negative load factors. Luckily, this is not the case, due to the bias of +1 g from the gravity. Therefore, for the purpose of structural load determination, the curve should be shifted by one unit upwards. Then the load factors are seen to have varied between -1.5 and +3.3.

 

 


Altitudes

 

In Figure 4, the altitude profile is shown for the time inteval 11.01.04 Z to 11.23.14 Z. It is clearly seen that the turbulence made keeping constant altitude impossible. It is also seen that the most troublesome turbulence occurred during the time interval 11.01 to 11.10. After that, there was a certain decrease in turbulence induced altitude fluctuations. On the other hand, the cloud base started decreasing.

Figure 4. Altitudes during the time interval of interest.

 

 

 

Turns

 

As has been seen above, several turns had to be performed to keep free of clouds and obstacles. In the table below, the most important turns are shown. Times indicate when the turn was initiated. It is seen that at about 11.10, there was a certain improvement in meterological conditions

 

Time

hh.mm.ss

Turn angle

degrees

Direction of turn

Final heading

degrees

11.01.34

29

Right

35

11.02.15

26

Left

10

11.03.49

31

Right

41

11.04.59

47

Left

354

11.06.54

51

Right

45

11.07.34

23

Left

22

11.08.24

21

Right

43

11.09.14

20

Left

23

11.10.04

16

Right

39

 

After the turns described in the table, only minor turns of typically ten degrees occurred. Those turns were essentially results of turbulence. The turn initiated at 11.10.04 brought the flight into the direction towards PAM. At about 11.20, the weather conditions worsened again and the flight was directed to an unplanned alternative.

 

The direction changes are shown in greater detail in Figure 5. There, headings west of north are shown as negative hedings.

 

Figure 5. Headings during the time period 11.00 - 11.23. Headings in the interval 181-359 degrees are shown as negative.

 

 

Quality of the record

 

During most of the time, data from ten satellites were received. The highest number occurred in the time interval 11.07.29 - 11.11.19 with eleven satellites. There was a fifteen seconds long interval close to 11.20 with down to eight satellites received. Then, the HDOP value increased to 1.2 as compared to 1.1 during the rest of the record.

 

 

 

 

Discussion

 

It is well known from statistics as well as from individual accident reports that VFR into IMC is extremely dangerous. Particularly, this is the case at low altitudes. In such a situation, there are two possible ways to minimize risks.

 

The first method is to request IFR clearance, and climb to safe altitude by entering clouds. In the present case, this could be used only as a last possibility if other methods failed. Although I have a demonstrated ability to fly on instuments for extended times, and am able to perform an ILS-approach, I am not sure that I am able to control the aircraft in clouds for an extended times if a considerable turbulence is present.

 

The second method is to use all skill and concentration upon keeping the aircraft under control, free of clouds, and to avoid obstacles. Nothing else should be allowed to split the attention. Even during a two seconds long look at the map, the turbulence could put the aircraft into a dive that from which recovery would be impossible at the low altitude in question. Also, such a short distraction could cause collision with an obstacle in the low visibility.

 

After a few of the turns seen in in the table above, all sense for position or direction was lost. When the visibility and turbulence situation started to improve, at about 11.10, the first action was to find the direction to PAM, and turn to that heading. By chance, I was already more or less at a reasonably correct heading, so merely minor adjustments were required. During the time interval 1110 - 11.23, the (diffuse) cloud base was gradually decreasing, and at 11.23, the decision was taken to turn 180 degrees and ask for vectors to a suitable airport.

 

 

 

Alinsĺs 2008-07-16

 

 

 

Allan Emrén