BroomstickPilot
5th Aug 2007, 22:50
Hi Guys,
I'm not an instructor, but I would like to draw to the attention of the instructor community a subject that I think is important but doesn't get the attention it deserves.
In a Private Flying thread, there is discussion about the tragic accident on the Isle of Wight. As was said on that thread, it would be wrong to speculate regarding the cause of that particular tragic accident until all the facts are known.
Nevertheless, inevitably the subject of operating in hot weather arose in that thread, and I thought that this presented an opportunity to open discussion on an important, and frequently overlooked, flight safety issue, namely operating in hot weather. This is why I have started this thread. Let me tell you about my 'ILAFFT' experience.
I recently revalidated my PPL after a break of very many years. I did all of my retraining in the UK and most of it during winter. Last year, I nearly had an accident precisely because I did not appreciate the full effect that hot weather could have not only on the performance, but also on the behaviour of a small, light, low powered aircraft.
I was flying an 80hp Sky Arrow VLA solo with no baggage but with full fuel from Old Sarum (285 feet a.m.s.l.) to Sandown at about 3 p.m. on the hottest day of the year, (and last year really was hot). As I recall, the wind was very light that day.
I commenced my takeoff roll as usual, but when I would be doing about 20 odd kts the aircraft suddenly slewed sharply 50 or 60 degrees to the left. I cut the power and applied the breaks to bring the aircraft to a halt. I assumed that my left main undercarriage wheel might have found an odd patch of soft ground on the grass runway but I was not sure. I checked the aircraft, but could find nothing wrong.
So I took the aircraft back onto the runway and commenced a new takeoff. This time the aircraft remained straight, but accelerated more slowly than usual and eventually staggered into the air but would hardly climb at all. At first, I thought I had forgotten to lower the flaps for takeoff, but looking round saw that the flaps were indeed where they were supposed to be. Once well clear of the ground, and into cooler air the rest of the flight was uneventful.
Safe on the ground at Sandown with a cool drink in my hand, I began to do a mental post mortem on the flight. My gliding experience of 40 years ago came to my aid. The first thing I realised was that the reason for the sudden slew was because a huge thermal must have gone up somewhere to my right, causing air to be sucked in suddenly, causing a sudden and strong localised cross wind gust. The Sky Arrow is very light and has a relatively huge tail fin and a free castoring nose wheel, so the gust must have caused her to 'weather-cock' left. (No doubt a Warrior, being heavier and with a steerable nosewheel, would have been much less affected).
I then worked out that the only thing that could have caused the slow acceleration and poor climb was thin air. Back at Old Sarum, I took out my whizz wheel, took the pressure altitude at time of takeoff and corrected it for temperature and worked out that my density altititude at take off must have been about 4,000 feet or more ISA!
In the days leading up to this incident, I had carried out three cross country flights that had all gone like clockwork. For some months previously, my cousin had indicated that she would like to come with me on one of my flights one day. I had thought hard about inviting her to come on my Sandown trip, but in the end decided against it. If she had flown with me on that day, one can only speculate on what the outcome might have been.
The point I am leading up to here is that had I trained in California or Florida, I probably wouldn't have been caught out as I was, as pilots in those places experience high density altitude throughout much of the year. In the UK, however, (at least until now,) we have never had a long summer season of hot weather, and most private pilots only fly about 50 hours annually spread through the year anyway.
Discussing this issue recently with a very experienced instructor, he commented that few UK PPLs would even be acquainted with the term 'density alititude'. I wonder if there is a training issue here that needs better handling? Perhaps on hot days we should have a notice over the door that leads to the apron saying, 'Make sure you calculate your density altitude and your TODR before you depart'.
This subject is now open to the floor.
Broomstick.
I'm not an instructor, but I would like to draw to the attention of the instructor community a subject that I think is important but doesn't get the attention it deserves.
In a Private Flying thread, there is discussion about the tragic accident on the Isle of Wight. As was said on that thread, it would be wrong to speculate regarding the cause of that particular tragic accident until all the facts are known.
Nevertheless, inevitably the subject of operating in hot weather arose in that thread, and I thought that this presented an opportunity to open discussion on an important, and frequently overlooked, flight safety issue, namely operating in hot weather. This is why I have started this thread. Let me tell you about my 'ILAFFT' experience.
I recently revalidated my PPL after a break of very many years. I did all of my retraining in the UK and most of it during winter. Last year, I nearly had an accident precisely because I did not appreciate the full effect that hot weather could have not only on the performance, but also on the behaviour of a small, light, low powered aircraft.
I was flying an 80hp Sky Arrow VLA solo with no baggage but with full fuel from Old Sarum (285 feet a.m.s.l.) to Sandown at about 3 p.m. on the hottest day of the year, (and last year really was hot). As I recall, the wind was very light that day.
I commenced my takeoff roll as usual, but when I would be doing about 20 odd kts the aircraft suddenly slewed sharply 50 or 60 degrees to the left. I cut the power and applied the breaks to bring the aircraft to a halt. I assumed that my left main undercarriage wheel might have found an odd patch of soft ground on the grass runway but I was not sure. I checked the aircraft, but could find nothing wrong.
So I took the aircraft back onto the runway and commenced a new takeoff. This time the aircraft remained straight, but accelerated more slowly than usual and eventually staggered into the air but would hardly climb at all. At first, I thought I had forgotten to lower the flaps for takeoff, but looking round saw that the flaps were indeed where they were supposed to be. Once well clear of the ground, and into cooler air the rest of the flight was uneventful.
Safe on the ground at Sandown with a cool drink in my hand, I began to do a mental post mortem on the flight. My gliding experience of 40 years ago came to my aid. The first thing I realised was that the reason for the sudden slew was because a huge thermal must have gone up somewhere to my right, causing air to be sucked in suddenly, causing a sudden and strong localised cross wind gust. The Sky Arrow is very light and has a relatively huge tail fin and a free castoring nose wheel, so the gust must have caused her to 'weather-cock' left. (No doubt a Warrior, being heavier and with a steerable nosewheel, would have been much less affected).
I then worked out that the only thing that could have caused the slow acceleration and poor climb was thin air. Back at Old Sarum, I took out my whizz wheel, took the pressure altitude at time of takeoff and corrected it for temperature and worked out that my density altititude at take off must have been about 4,000 feet or more ISA!
In the days leading up to this incident, I had carried out three cross country flights that had all gone like clockwork. For some months previously, my cousin had indicated that she would like to come with me on one of my flights one day. I had thought hard about inviting her to come on my Sandown trip, but in the end decided against it. If she had flown with me on that day, one can only speculate on what the outcome might have been.
The point I am leading up to here is that had I trained in California or Florida, I probably wouldn't have been caught out as I was, as pilots in those places experience high density altitude throughout much of the year. In the UK, however, (at least until now,) we have never had a long summer season of hot weather, and most private pilots only fly about 50 hours annually spread through the year anyway.
Discussing this issue recently with a very experienced instructor, he commented that few UK PPLs would even be acquainted with the term 'density alititude'. I wonder if there is a training issue here that needs better handling? Perhaps on hot days we should have a notice over the door that leads to the apron saying, 'Make sure you calculate your density altitude and your TODR before you depart'.
This subject is now open to the floor.
Broomstick.