When to Enter Ihram on a Plane
Question

I work on private planes. People travel with us and we take them from one region to another. During one trip we were heading towards Jeddah and some men travelled with us who were heading to Makkah. They said to us: “When we arrive above the miqat, tell us.” But we forgot to tell them and we did not remind them. When there was only a short time left before we reached Jeddah, I remembered them and I asked the captain, and he said: “Tell them that we are over the miqat now.” Do they have to do anything? And if so, what do they have to do? And who bears the sin?.
Praise be to Allah.Locations for ihram
The Prophet (blessings and peace of Allah be upon him) defined the locations of the miqats in a hadith narrated by Ibn 'Abbas (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings of Allah be upon him) defined the miqat of the people of Madinah as Dhu’l-Hulayfah; that of the people of Sham (Syria) as al-Juhfah; that of the people of Najd as Qarn al-Manazil; and that of the people of Yemen as Yalamlam. And he said: “And these miqats are for the people at those very places, and for others who come through those places with the intention of performing Hajj and ‘Umrah; and whoever is living within these boundaries can enter ihram from the place from which he sets out, and the people of Makkah can start (and enter ihram) from Makkah.” (Narrated by al-Bukhari, no. 1254; Muslim, no. 1181) 
The jurists are unanimously agreed upon these miqats and that they are for their people and for those who come to them. (See al-Ishraf by Ibn al-Mundhir, 3/177; Maratib al-Ijma‘, p. 42; al-Istidhkar, 11/76; al-Mughni, 5/56) 
Can you pass the miqat without ihram?
Based on this, it is not permissible for the one who intends to do Hajj or `Umrah to pass the miqat that is prescribed for him , whether he is coming by land or sea or air, because of the report narrated by Ibn `Umar (may Allah be pleased with him) who said: When these two regions were conquered, they came to ‘Umar and said: O Amir al-Mu’minin, the Messenger of Allah (blessings and peace of Allah be upon him) defined Qarn (as the miqat) for the people of Najd, but it is out of our way and if we want to go to Qarn it is difficult for us. He said: Look and see where on their route is in line with it, and he identified Dhat ‘Irq for them (as their miqat). (Narrated by al-Bukhari, 1531) 
‘Umar (may Allah be pleased with him) made the miqat of those who did not pass by the (original) miqat a place that was in line with it, and whoever comes in line with it by air is like the one who comes in line with it on land. 
How do you put on Ihram on a plane?
So what the one who comes in line with the miqat when he is on the plane must do is enter ihram . It is better for him to enter ihram before he comes in line with it, because of the speed with which the plane travels. 
With regard to the people you asked about, what they should have done was to put on the ihram garments and recite the Talbiyah for ‘Umrah or Hajj, and if they had already put on the ihram garments, they would not have had to do anything but recite the appropriate Talbiyah as soon as you told them that they had reached the miqat, and they would not have had to do anything more than that, so long as they did not deliberately pass the miqat without entering ihram. They did not know at all that they had passed it without entering ihram; rather they thought that the place from which they should enter ihram was their miqat, based on what you told them. 
In your case, what you should have done was wake them up before reaching the miqat , allowing enough time for them to prepare to enter ihram. This was a matter that was entrusted to you and was your responsibility. 
As you forgot to do that, there is no sin on them for what they forgot, because Allah, may He be exalted, says (interpretation of the meaning):
“Allah burdens not a person beyond his scope. He gets reward for that (good) which he has earned, and he is punished for that (evil) which he has earned. ‘Our Lord! Punish us not if we forget or fall into error, our Lord! Lay not on us a burden like that which You did lay on those before us (Jews and Christians); our Lord! Put not on us a burden greater than we have strength to bear. Pardon us and grant us Forgiveness. Have mercy on us. You are our Maula (Patron, Supporter and Protector, etc.) and give us victory over the disbelieving people’” [al-Baqarah 2:286].  
According to the hadith qudsi, Allah, may He be exalted, says: “I have granted that.” (Narrated by Muslim, 126) 
Abu Dharr al-Ghifaari said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Allah has forgiven for my ummah their mistakes and forgetfulness, and what they are forced to do.” (Narrated by Ibn Majah, 2043; classed as sahih by al-Albani) 
But the big problem with your case is that you should have told them about the real situation and that you had in fact passed the miqat. In that case they should have delayed their ihram until they got off the plane , then went back to the miqat and entered ihram from there. 
If they entered ihram knowing that they had passed the miqat, then they should have sacrificed a fidyah (ransom). 
In fact, the sin that you committed, you and the captain, is in your having deceived them and not told them what had really happened. As it is no longer possible to put things right, then you – you yourself and those who were also part of it – have to repent to Allah, may He be exalted, for having deceived them, especially since the matter has to do with the validity of an act of worship and the sacred limits set by Allah in that regard. 
As well as repenting to Allah, may He be exalted, from that, you also have to work out the number of these pilgrims who went to do ‘Umrah, even if it is only an approximation, and slaughter a hadiy (sacrificial animal) for each one of them, because you are the ones who caused them to pass the miqat with you without entering ihram, then you denied them the opportunity to go back and make up what they had missed. 
Passing the miqat without ihram: what to do?
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked about a group of people who went for Hajj on mass transit, and the driver did not tell them about the miqat until one hundred kilometers after they had passed it. The passengers asked him to go back to the miqat so that they could enter ihram from there, but he refused to go back and the trip continued until they reached Jeddah . What do they have to do? 
He replied: 
“What the driver should do is stop at the miqat so that the people can enter ihram from there. If he forgot and did not remember until after one hundred kilometers, as the questioner said, he has to take the people back so that they can enter ihram from the miqat , because he knows that these people want to do ‘Umrah or Hajj. So if he does not do that and they enter ihram from where they are, i.e., one hundred kilometers after passing the miqat, then each one of them has to offer a fidyah (ransom), a sacrifice to be slaughtered in Makkah and its meat distributed to the poor, because they omitted one of the obligatory actions of the rituals, whether for Hajj or ‘Umrah. 
In this case, if they took the matter to court, perhaps the court would rule that he is liable for the cost of this fidyah , because he is the one who caused them to have to pay that penalty. This matter should be referred to the court; if the judge thinks that it is appropriate, he may say to the driver: You have to pay the value of the fidyahs that these people slaughtered, because you are the one who transgressed against them; you were the one who forgot and you were careless first of all, that you transgressed against them a second time by depriving them of the right to go back (to the miqat).” (Majmu‘ Fatawa al-Shaykh, 21/368) 
And Allah knows best.